UC-NRLF 


302 


• , BERKELEY 

I        .RY 

UNIVERSITY   OF 
CALIFORNIA 


SCIENCES 


ELEMENTS   OF 

•MINERALOGY,  CRYSTALLOGRAPHY 
-  AND   BLOWPIPE  ANALYSIS- 

FROM   A   PRACTICAL   STANDPOINT 

INCLUDING 

A  DESCRIPTION  OF  ALL  COMMON  OR  USEFUL  MINERALS,  THEIR 
FORMATION  AND  OCCURRENCE,  THE  TESTS  NECESSARY  FOR 
THEIR  IDENTIFICATION,  THE  RECOGNITION  AND  MEAS- 
UREMENT OF  THEIR  CRYSTALS,  AND  THEIR 
ECONOMIC  IMPORTANCE  AND  USES 
IN  THE  ARTS 


BY 

ALFRED    J.    I^OSES,  E.M.,  PH.D. 

Professor  of  Mineralogy,  Columbia  University,  New  York  City 
AND 

CHARLES    LATHROP    PARSONS,  D.Sc.,  D.CHEM, 

Chief  Chemist  United  States  Bureau  of  Mines 


FIFTH  EDITION 
ENLARGED  ANJD  IN  LARGE  PART  REWRITTEN 


'      'NEW  YORK 

D.  VAN   NOSTRAND   COMPANY 
25   PARK  PLACE 

1916 


Ft  I 


JCIENCES 


Entered  according  to  the  Act  of  Congress  in  the  year  1916,  by 

A.    J.    MOSES  AND  C.   L.    PARSONS 
In  the  Office  of  the  Librarian  of  Congress.     All  rights  reserved. 


PRESS  OF 

THE  NEW  ERA  PRINTING  COMPANY 
LANCASTER.  PA 


PREFACE. 


In  this,  the  fifth  edition  of  our  textbook,  the  "practical  stand- 
point" of  the  former  editions  is  maintained  and  skill  in  "Sight 
Recognition  and  Rapid  Determination  of  Common  and  Econom- 
ically Important  Minerals"  is  still  the  chief  objective. 

About  two  hundred  additional  pages  have  been  needed  and 
the  changes,  while  distributed,  are  principally: 

(a)  Descriptions  of  new  economic  groups  and  species  consequent 
on  the  great  development  in  industrial  applications. 

(b)  Discussions  of  formations  and  occurrences,  in  recognition 
of  the  growing  interest  in  mineral  genesis  and  of  its  value  both  in 
diagnosis  and  in  connecting  more  closely  geology  and  mineralogy. 

(c)  An    enlarged     section    on     crystallo-optics,    schemes     for 
crushed   fragments  and  grouped  optical  distinctions  consequent 
upon  the  proved  value  of  the   polarizing  microscope    in  rapid 
mineral  determinations. 

(d)  New  tables  for  determination. 

Two  other  new  features  may  be  mentioned : 

1.  In   the  introductory  chapter,   as  a  substitute  for  the  usual 
crystallo graphic  course  involving  symbols  and  axes,  we  have  given 
a  simplified  method  of  classifying  and  identifying  real  crystals 
by  partial  symmetry  and  angles  which  enables  the  student  after 
two  or  three  lessons  to  recognize  the  crystalline  system  of  real 
crystals  and  often  to  identify  the  species  by  simple  measurements. 

2.  The  gem  minerals  have  been  assembled  and  described  in  a 
separate  chapter. 


3G0415 


TABLE   OF   CONTENTS. 


PREFACE iii 

BIBLIOGRAPHY xi 

PART    I.   CRYSTALLOGRAPHY.    CHAPTERS  I.  TO  X.,  PAGES   i  TO  156. 

CHAPTER  I.     Introductory i  to  27 

Crystals  and  Their  Angles I 

Contact  Goniometers .,..  3 

Approximate  Measurements .    .  5 

Symmetry  and  Classification 6 

Determination  of  Crystals  by  Partial  Sym- 
metry and   Approximate  Angles 12 

By  Crystal  Axes  and  Symbols 20 

Crystal  Structure 26 

II  to  VII.     The  "Systems,"  Their  Classes,  Forms  and 

Symbols 28  to  66 

The  Triclinic  System 28 

The  Monoclinic  System 32 

The  Orthorhombic  System 36 

The  Tetragonal  System 42 

The  Hexagonal  System 48 

The  Isometric  System 58 

VIII.     The  Grouping  of  Crystals  and  Their  Imperfec- 
tions   68  to  81 

Twin  Crystals 68 

Crystal  Aggregates 70 

Terms  of  Growth  and  Habit 74 

Irregularities  of  Faces 77 

Internal  Peculiarities 79 

Intergrowths  and  Parallel  Growths 81 

IX.     The    Determination   of   the   Geometrical 

Constants  of  a  Crystal 82  to  95 

Measurement  of  Interfacial  Angles 82 

Stereographic  Projections 84 

V 


vi  TABLE    OF  CONTENTS. 

Symmetry  and  Elemental  Faces 87 

Zonal  and  Graphic  Determination  of  Indices  88 

Calculation  of  Axial  Elements 91 

Crystal  Drawing 92 

X.     Crystals-Optics 96  to  155 

Light  and  Its  Fundamental  Phenomena.  ...  96 

Optically  Isotropic  and  Anisotropic  Crystals  99 
Double  Refraction  and  Polarization  in  Cal- 

cite 100 

Optically  Uniaxial  Crystals 102 

Optically  Biaxial  Crystals 105 

Production  of  Plane  Polarized  Light 107 

The    Polarizing    Microscope    and    Its  Ad- 
justments   117 

Preparation  of  Material  for  Optical  Testing  125 

Determining  Isotropic  or  Anisotropic 127 

Determining  Indices  of  Refraction 127 

Determining  Sign  of  Elongation 134 

Determining  Birefringence 135 

Determining  Isotropic  Uniaxial  or  Biaxial .  140 
Determining  the  Character  of  Double  Re- 
fraction   145 

Determining  Angle  between  Optic  Axes .  .  .  147 
Determining    the     Crystalline    System    by 

Optical  Tests 150 

Absorption,  Color  and  Pleochroism 151 

Determining  Pleochroism 153 

PART  II.     BLOWPIPE  ANALYSIS.     CHAPTERS  XL  TO  XIV.  Pages  156  to  207. 

XL     Apparatus  Blast,  Flame,  Etc 156  to  163 

XII.     Operations  of  Blowpipe  Analysis 164  to  181 

XIII.  Summary    of    Useful    Tests    with    the 

Blowpipe 182  to  196 

XIV.  Schemes  for  Qualitative  Blowpipe  An- 

alysis      197  to  200 

PART  III.     MINERALOGY.     CHAPTERS  XV  to  XXI     Pages    208  to  549. 
XV.     Definition  and  Physical  Characters. .  .   208  to  230 


TABLE    OF   CONTENTS.  vii 

XVI.     The  Chemical  Characters  of  Minerals.  .  231  to  238 

XVII.     Formation  and  Occurrence 239  to  260 

XVIII.     The  Minerals  of  the  Metalliferous  Ore 

Deposits 261  to  416 

The  Iron  Minerals 261 

The  Manganese  Minerals 277 

The  Cobalt  and  Nickel  Minerals 286 

The  Zinc  and  Cadmium  Minerals 295 

The  Tin  Minerals :   304 

The  Titanium  Minerals 308 

The     Zirconium,     Thorium,     Cerium     and 

Yttrium  Minerals 310 

The  Lead  Minerals 316 

The  Bismuth  Minerals 324 

The  Arsenic  Minerals , 327 

The  Antimony  Minerals 332 

The  Vanadium  Minerals 336 

The  Uranium  and  Radium  Minerals.  .....   341 

The  Chromium  Minerals 345 

The  Molybdenum  Minerals 348 

The  Tungsten  Minerals 350 

The  Columbium  and  Tantalum  Minerals.  .   354 

The  Copper  Minerals 357 

The  Mercury  Minerals 373 

The  Silver  Minerals 37& 

The  Gold  Minerals. 392 

The  Platinum  Group  Minerals 401 

The  Aluminum  Minerals 406 

XIX.     Minerals   Important  in   the   Industries 

and  Not  Already  Described 417  to  478 

The  Potassium  Minerals 417 

The  Sodium  Minerals 421 

The  Lithium  Minerals 428 

The  Ammonium  Minerals 430 

The  Barium  Minerals 431 

The  Strontium  Minerals 434 

The  Calcium  Minerals 437 

The  Magnesium  Minerals 450 


viii  TABLE    OF   CONTENTS. 

The  Boron  Minerals 454 

The  Minerals  of  Chlorine,  Bromine,  Iodine 

and  Fluorine 459 

The  Sulphur  Minerals 460 

The  Selenium  and  Tellurium  Minerals 464 

The  Hydrogen  Minerals 465 

The  Nitrogen  Minerals 466 

The  Phosphorus  Minerals 467 

The  Carbon  Minerals 472 

XX.     Silica  and  the  Rock- Forming  Silicates .   479  to  549 

Silica 482 

The  Feldspars 488 

The  Feldspathoids 497 

The  Pyroxene  and  Amphibole  Groups 500 

Garnet 509 

Vesuvianite 511 

The  Olivine  Group 512 

The  Scapolite  Group 515 

The  Andalusite  Group 517 

Staurolite 520 

Beryl,  Topaz  and  Tourmaline 521 

Titanite , 525 

The  Epidote  Group 526 

The  Zeolite  Group 529 

The  Mica  Group 537 

The  Chlorite  Group 541 

The  Hydrous  Silicates  of  Magnesium 543 

The  Hydrous  Silicates  of  Aluminum 547 

XXI.  Minerals  Used  as  Precious  and  Orna- 

mental Stones 550  to  579 

Transparent  Stones 550 

Translucent  to  Opaque  Stones 570 

PART    IV.     DETERMINATIVE    MINERALOGY. 

XXII.  Tables  for  the  Rapid  Determination  of 

the  Common  Minerals 580  to  614 

Explanatory 580 

Key '. 585 


TABLE    OF  CONTENTS.  ix 

Minerals  of  Metallic  or  Submetallic  Lustre .  586 

Minerals  of  Non-metallic  Lustre.  594 

A.  By  Blowpipe  and  Physical  Characters 

B.  By  Aid  of  Polarizing  Microscope 

Table  of  Atomic  Weights 614 

General  Index 6l5 

Index  to  Minerals 625 


BIBLIOGRAPHY. 


It  is  not  proposed  to  offer  a  complete  bibliography  but  simply 
to  name  a  few  standard  and  usually  recent  works  in  each  division 
of  the  subject. 

Treatises,  Mineralogy. 

Dana,  J.  D.     System  of  Mineralogy,  6th  edition,  with  three  appendices  (1899, 

1909  and  1915).     John  Wiley  &  Sons,  N.  Y.,  1892. 
Hintze,  Carl.     Handbuch  der  Mineralogie.     Bd.  i,  1904;  Bd.  2,  1897.     vonVeit 

&  Co.,  Leipzig.     (Still  incomplete.) 
Text  Books,  Mineralogy. 

Bauer,    M.     Lehrbuch    der    Mineralogie.     2d    ed.     1904.     E.    Schweizbart., 

Stuttgart. 
Dana-Ford.     Manual  of  Mineralogy.     i3th  edition.     John  Wiley  &  Sons,  N.  Y., 

1912. 
Miers,  H.  A.     Mineralogy.     An  Introduction  to  the  Scientific  Study  of  Minerals. 

Macmillan  &  Co.,  London,  1902. 
Naumann-Zirkel.     Elemente  der  Mineralogie.     I3thed.     1898.    W.  Engelmann, 

Leipzig. 

Phillips,  A.  H.     Mineralogy.     The  Macmillan  Co.,  New  York,  1912. 
Rogers,  A.  F.     Introduction  to  the  Study  of  Minerals.     McGraw-Hill  Book  Co., 

N.  Y.,  1912. 

Tschermak,  G.     Lehrbuch  der  Mineralogie.     6th  ed.     1905.     A.  Holder,  Wien. 
Determinative  Mineralogy  and  Blowpipe  Analysis. 

Brush-Penfield.     Manual  of  Determinative  Mineralogy.     i6th  edition.     John 

Wiley  &  Sons,  N.  Y.,  1906. 

Eakle,  A.  S.     Mineral  Tables.     John  Wiley  &  Sons,  N.  Y.,  1904. 
Fuchs-Brauns.     Anleitung    zum     Bestimmen    der    Mineralien.     6th    ed.     A. 

Topelmann,  Giessen,  1913. 
Frazer-Brown.     Tables  for  the  Determination  of  Minerals.     6th  edition.     J.  B. 

Lippincott  Co.,  Philadelphia,  1910. 
Kraus-Hunt.     Tables  for  the  Determination  of  Minerals.     McGraw-Hill  Book 

Co.,  N.  Y.,  1911. 
Lewis,  J.  V.     Determinative  Mineralogy.     2d  ed.     John  Wiley  &  Sons,  N.  Y., 


Plattner- Kolbeck.     Probierkunst  mit  der  Lotrohre.     7th  edition.    Johann  Earth 

Leipzig,  1907. 
Chemical  Mineralogy. 

Brauns,  R.     Chemische  Mineralogie.     Tauchnitz,  Leipzig,  1896. 

Doelter,  C.     Physikalische-Chemische  Mineralogie.     J.  A.  Earth,  Leipzig,  1905, 

Doelter,  C.     Handbuch   der  Mineral   Chemie,   Bd.   I,   II,   III.     T.   Sternkopf. 

Dresden,  1912-1913. 
Microchemical  Analysis. 

Chamot,  E.  M.     Elementary  Chemical  Microscopy.     John  Wiley  &  Sons,  N.  Y., 

1916. 


xii  BIBLIOGRAPHY. 

Occurrence,  Association  and  Origin  of  Minerals. 

Beyschlag-Krusch-Vogt.     (Translated  by  S.  J.  Truscott.)     The  Deposits  of  the 

Useful  Minerals  and  Rocks,  Vol.  i,  1914;   Vol.  2,  1916;   Vol.  3,  .     Mac- 

millan  &  Co.,  London. 
Clarke,  F.  W.     The  Data  of  Geochemistry.     Bulletin  No.  660,  U.  S.  Geol. 

Surv.,  1915. 

Leith  and  Meade.     Metamorphic  Geology.     Henry  Holt  &  Co.,  1915. 
Lindgren,  W.     Mineral  Deposits.     McGraw-Hill  Book  Co.,  1913. 
Van  Hise,  C.  R.     A  Treatise  on  Metamorphism.     Monograph  47,  U.  S.  Geol. 

Surv.,  1904. 
Weinschenck,  E.      Grundziige  der  Gesteinskiinde,  Herder.  Freiburg  im  Bries- 

gau,  1905. 
Rock  Minerals  and  Their  Microscopic  Examination. 

Iddings,  J.  P.     Rock  Minerals.     2d  edition.     John  Wiley  &  Sons,  N.  Y.,  1912. 
Johannsen,   A.     Determination   of   Rock   Forming   Minerals.     John  Wiley  & 

Sons,  N.  Y.,  1908. 
Johannsen,  A.     Manual  of  Petrographic  Methods.     McGraw-Hill  Book  Co., 

1914. 
Luquer,  L.  Mel.     Minerals  in  Rock  Sections.     4th  edition.     D.  Van  Nostrand 

Co.,  1913. 
Weinschenck-Clark.     Petrographic  Methods.     McGraw-Hill  Book  Co.,  N.  Y., 

1912. 
Wright,  F.  E.     The  Methods  of  Petrographic-Microscopic  Research.     Carnegie 

Institution,  1911. 
Microscopic  Study  of  Minerals. 

Murdoch,   J.     Microscopical   Determination  of   the   Opaque   Minerals.     John 

Wiley  &  Sons,  N.  Y.,  1916. 
Schroeder  van  der  Kolk,  J.  L.  C.     Tabellen  zur  mikroskopischen  Bestimmung 

der   mineralien    nach    ihren     Brechnungsexponenten.     2d    edition.     C.    W. 

Kreidel,  Wiesbaden,  1906. 
Seeman,  F.     Leitfaden  der  Mineralogischen  Bodenanalyse.     W.  Braunmiiller, 

1914. 
Winchell-Winchell.     Elements  of  Optical  Mineralogy.     D.  Van  Nostrand  Co., 

N.  Y.,  1908. 
Rare  Minerals. 

Cahen  and  Wootton.     The  Mineralogy  of  the  Rarer  Metals.     J.  B.  Lippincott 

Co.,  Philadelphia,  1912. 
Gems  and  Precious  Stones. 

Bauer,  Max.     Edelsteinkunde.     2d  edition.     Tauchnitz,  Leipzig. 
Cattelle,  W.  R.     Precious  Stones.     J.  B.  Lippincott  Co.,  Philadelphia,  1903. 
Crookes,  Sir  Wm.     Diamonds.     Harper  Bros.,  N.  Y.,  1909. 
Escard,  J.     Les  Pierres  Prccieuses.     Dunod  et  Pinat,  Paris,  1914. 
Farrington,  O.  C.     Gems  and  Gem  Minerals.     A..W.  Mumford,  Chicago,  1903. 
Eppler,  A.     Die  Schmuck  und  Edelsteine.     Felix  Krais,  Stuttgart,  1912. 
Smitn,  G.  F.  II.     Gem  Stones.     James  Pott  &  Co.,  N.  Y.,  1912. 
Crystallography  (Geometrical). 

Bayley,  W.  S.     Elementary  Crystallography.     McGraw-Hill  Book  Co.,  N.  Y., 

1910. 
Hilton,  H.     Mathematical  Crystallography.     Clarendon  Press,  Oxford,   1903. 


BIBLIOGRAPHY.  xiii 

Lewis,  W.  J.  A.     A  Treatise  on  Crystallography.     University  Press,  Cambridge, 

Eng.,  1899. 

Linck,  G.     Grundriss  der  Kristallographie,  3d  ed.     G.  Fischer,  Jena,  1913. 
Tutton,    A.    E.    H.     Crystallography    and    Practical    Crystal    Measurement. 

Macmillan  &  Co.,  London,  1911. 

Viola,  C.  M.     Grundziige  der  Kristallographie.     W.  Engelmann,  Leipzig,  1906- 
Walker,  T.  L.     Crystallography.     McGraw-Hill  Book  Co.,  N.  Y.,  1914. 
Crystallography  (Physical  and  Chemical). 

Becker,  A.     Krystalloptik.     F.  Erike,  Stuttgart,  1903. 

Fletcher,  L.     The  Optical  Indicatrix.     H.  Frowde,  London,  1892. 

v.  Groth,  P.     Chemische  Krystallographie.     3  vols.     W.  Engelmann,  Leipzig, 

1910. 
v.  Groth,  P.     Physikalische   Krystallographie.     W.   Engelmann,   Leipzig,   also 

translation  of  part  by  Jackson.     John  Wiley  &  Sons,  N.  Y.,  1910. 
Groth-Marshall.     Introduction  to  Chemical  Crystallography.     John  Wiley  & 

Sons,  N.  Y.,  1906. 

Tamman,  G.     Kristallisiren  und  Schmelzen.     J.  A.  Earth,  Leipzig,  1903. 
Voigt,  W.     Elemente  der  Krystallphysik.     von  Veit  &  Co.,  Leipzig,  1898. 
Crystal  Structure. 

Bragg,  W.  H.  &  W.  L.     X-Rays  and  Crystal  Structure.     G.  Bell  and  Sons, 

London,  1915. 

Pope,  W.  J.     Annual  Report  Chemical  Society  London,  p.  258.     London,  1908. 
Schonflies,  A.     Krystallsysteme  und  Krystallstructur.     B.  G.  Teubner,  Leipzig, 

1891. 
Sohnke,  L.     Entwickelung  einer  Theorie  der  Krystallstructur.     B.  G.  Teubner, 

Leipzig,  1879. 
Story-Maskelyne  and  Others.     Report  Committee  of  British  Association  for 

Advancement  Science,  1901. 
Tutton,  A.  E.   H.     Crystalline  Structure  and  Chemical  Constitution.     Mac- 

millan &  Co.,  London,  1910. 
Liquid  Crystals. 

Lehmann,  O.     Fliissige  Kristalle.     W.  Engelmann,  Leipzig,  1904. 

Schenck,  R.     Kristallinische  Fliissigkeiten  und  Fliissige  Kristalle.     W.  Engel- 

mann, 1905. 
The  Uses  of  Minerals. 

Dammer  und  Tietze.     Die  Nutzbaren  Mineralien.     2  vols.     F.  Enke,  Stuttgart, 


Mineral  Resources  of  the  United  States.     Annually  since  1883.     U.  S.  Geol. 

Survey. 

The  Mineral  Industry.     Annually  since  1892.     McGraw-Hill  Book  Co.,  N.  Y. 
Engineering  and  Mining  Journal,  especially  Annual  Review  number. 
History  of  Mineralogy. 

Fletcher,  L.     Guide  to  Mineral  Collection  of  British  Museum. 
v.  Kobell,  F.     Geschichte  der  Mineralogie.     J.  G.  Cotta,  Miinchen,  1864. 
Mineral  Synonyms'. 

Chester,  A.  H.     Dictionary  of  the  names  of  Minerals.     John  Wiley  &  Sons, 

N.  Y.,  1896. 

Egleston,    T.     Catalogue    of    Minerals    and    Synonyms.     Washington,    Govt. 
Printing  Office,  1887. 


PART  I. 


CRYSTALLOGRAPHY. 


CHAPTER  I. 

INTRODUCTORY. 

The  meaning  of  the  word  crystal  in  ancient  times,  and  even  in 
the  English  of  the  Middle  Ages,  was  ice.  Transparent,  colorless 
quartz  was  called  crystal  because  it  was  supposed  to  be  ice  in 
permanent  form,  the  solids  obtained  on  the  evaporation  of  water 
were  crystal,  because  like  ice,  they  were  solids  formed  from  water. 

The  Common  Limited  Meaning  of  Crystal. 

Both  the  quartz  and  the  solid  salts  from  solutions  occurred  in 
shapes  bounded  by  plane  surfaces,  and  as  other  substances  both 
opaque  and  transparent  possessed  such  shapes,  by  an  extension 
of  meaning  crystal  came  to  signify  a  shape  bounded  by  plane  faces, 
and  more  exactly,  crystals,  in  this  limited  sense,  are  solids,  formed 
only  when  a  chemical  element  or  a  chemical  compound  solidifies, 
and  bounded  by  plane  faces  at  definite  angles  to  each  other  which 
are  characteristic  of  the  substance. 

The  Broader  Meaning  of  Crystal, 

It  is  known  now  that  this  "polyhedral"  shape  is  due  to  definite 
internal  structure  and  that  this  structure  is  of  such  a  nature  that 
a  "crystal"  always  shows  the  same  physical  characters*  in  all 
parallel  directions  and,  generally  speaking,  different  characters 
in  different  directions. 

*  For  instance,  crystals  will  often  break  in  directions  parallel  to  planes  yielding 
solids  absolutely  constant  in  angles,  they  will  transmit  light  or  conduct  heat  or  elec- 
tricity with  the  same  velocity  along  all  parallel  lines,  but  with  different  velocity 
along  lines  not  parallel. 


2  C7?  YSTALLOGRAPHY. 

But  solidified  chemical  substances  consist,  for  the  most  part, 
of  crowded  aggregations  of  individuals  with  little  or  no  trace  of 
plane-faced  boundaries.  Every  grain,  nevertheless,  possesses  the 
perfect  regular  internal  structure  with  the  physical  characters 
constant  in  parallel  directions  and  varying  in  directions  not 
parallel,  and  often  in  earlier  stages  of  growth  did  possess  the 
polyhedral  shape  until  crowding  obliterated  it. 

The  broad  definition  of  crystal  must  therefore  include  these 
individuals.  That  is,  crystals  are  distinct  individual  solids  resulting 
from  the  solidification  of  a  chemical  substance  and  showing  constancy 
of  properties  in  parallel  directions  and  varying  properties  in  direc- 
tions not  parallel. 

Under  favorable  conditions  of  free  space,  time  and  surroundings 
crystals  will  be  bounded  by  plane  surfaces  at  definite  angles  to  each 
other  and  characteristic  of  the  substance. 

Crystallization. 

Crystallization  is  therefore  that  solidification  of  a  chemical 
element  or  compound  which  results  in  individuals  possessing  a 
crystal  structure.  These  individuals  may  be  completely  bounded 
by  plane  surfaces  or  partially  bounded  by  plane  surfaces,  or  may 
lack  all  plane  boundaries.  They  are  identical  in  essentials  and 
there  is  no  line  of  division  in  the  non-essentials. 

GEOMETRICAL  CRYSTALLOGRAPHY.* 

Crystallography  is  broadly  divided  into: 

Geometrical  or  Morphological  Crystallography. 
Physical  Crystallography. 
Chemical  Crystallography. 

Of  these  this  book  considers  only  those  portions  of  the  first  two 
which  experience  has  proved  to  be  most  useful  in  the  identification 
and  description  of  minerals. 

Geometrical  crystallography  considers  the  relations  between 
the  bounding  faces. 

In  elementary  work  the  principal  tasks  are  determinations  of 
"system,"  recognition  of  type  symbols,  approximate  angle  meas- 

*  Geometrical  Crystallography  often  receives  an  unmerited  proportion  of  the  time 
devoted  to  the  study  of  crystals  as  a  natural  result  of  the  fact  that  the  geometrical 
relations  were  first  studied. 


INTR  OD  UCTOR  Y.  3. 

urements,  and,  perhaps  most  important,  interpretation  of  crystal 
descriptions. 

In  more  advanced  work  the  tasks  are  exact  measurements  of 
angles,  projection  and  delineation,  determination  of  indices  and 
elements  (axial  angles  and  parameters)  and  calculation  of  the- 
oretical angles  from  elements  and  indices. 

The  Angles'  of  Crystals. 

In  any  crystal  three  sorts  of  angles  exist: 

1.  Plane  angles  between  "edges"  (intersections  of  faces). 

2.  Dihedral  or  interfacial  angles. 

3.  Polyhedral  angles  between  three  or  more  planes. 

While  all  of  these  are  characteristic  the  interfacial  angles  are 
most  conveniently  used. 

Single  crystals  show  only  salient  angles,  re-entrant  angles  are 
common  on  twinned  crystals. 

Law  of  Constancy  of  Interfacial  Angles. 

The  angles  of  crystals  of  any  one  substance  conform  to  the 
following  law:  In  all  crystals  of  the  same  substance  the  angles 
between  corresponding  faces  are  constant. 

This  law,  the  first  to  be  announced,  was  gradually  developed;  for  instance, 
Steno  in  1669  announced  that  in  rock  crystal  there  was  no  variation  of  angle  in  spite 
of  the  variation  in  relative  size  of  the  faces.  In  1704  Guglielmini  stated  that  every 
salt  had  its  peculiar  crystals,  the  angles  of  which  were  constant 

Rome  Delisle  in  1783  measured  and  described  over  four  hundred  crystal  forms  and 
announced  that  in  each  species  "the  respective  inclination  of  the  faces  to  each  other 
never  varies." 

Aside  from  the  crystals  of  the  isometric  system  it  is  now  held 
to  be  true  that  the  crystals  of  each  chemical  substance  have  a 
separate  and  definite  set  of  angles,  certain  so-called  isomorphous 
substances  crystallizing  however  with  very  nearly  the  same 
angles. 

Contact  Goniometers. 

Measurements  within  one  or  two  degrees  may  be  made  with 
Contact  goniometers,  the  most  simple  type  of  which  consist  of  an 
arm  pivoted  upon  a  protractor.  Fig.  I  shows  Penfield  Goniometer 
Model  B,  consisting  of  a  cardboard  on  which  is  printed  a  semicircle 
graduated  from  o°  to  180°  in  both  directions. 


4  CRYSTALLOGRAPHY. 

An  arm  of  transparent  celluloid  is  swivelled  by  means  of  an  eyelet 
exactly  in  the  center  of  the  semicircle  tightly  enough  to  turn  with 
some  difficulty. 

FIG.  i. 


FIG.  2. 


In  measuring,  the  crystal  or  model  is  placed  as  shown  so  that 
the  card  edge  and  swinging  arm  are  each  perpendicular  to  the  edge 
of -intersection  of  the  two  faces,  and  in  such  close  contact  that 
no  light  passes  between  these  and  the  faces.  To  facilitate  this 

one  part  of  the  swinging  arm 
and  the  base  edge  of  the 
card  are  blackened. 

A  more  expensive  instru- 
ment, Fig.  2,  consists  of  a 
brass  protractor  with  detach- 
able arms  which  can  be  slid 
upon  the  pivot  until  of  the 
most  convenient  length  for 
the  particular  crystal, 

In  measuring  the  arms  are 
detached  and  set  at  an  angle 

a  little  less  than  the  angle  to  be  measured,  clamped  loosely  and 
one  of  the  arms  placed  in  perfect  contact  with  one  crystal  face. 
The  other  arm  then  nearly  touches  the  second  face  and,  while 
holding  between  the  eye  and  the  light,  is  brought  into  perfect 


INTR  OD  UCTOR  Y.  5 

parallelism  with  the  second  face  by   a  gentle  pressure  with  the 
forefinger. 

The  arms  are  then  replaced  on  the  arc,  as  in  the  figure,  and  the 
angle  is  read. 

THE   APPROXIMATE    MEASUREMENT   OF   INTERFACIAL   ANGLES. 

Determinations  of  symmetry,  system,  type  symbols,  and  ap- 
proximate angles,  of  sufficient  accuracy  to  greatly  help  in  the 
recognition  of  mineral  species,  can  be  made  with  very  simple 
apparatus  and  even  without  apparatus. 

In  many  cases  the  task  is  not  so  much  to  ascertain  the  value 
of  the  angles  as  to  estimate  the  equality  or  inequality  of  different 
angles  and  the  parallelism  of  faces  to  each  other  or  to  certain  lines. 

By  Inspection  Alone. 

Estimates  are  best  made  by  placing  the  two  crystal  faces  con- 
cerned at  right  angles  to  a  horizontal  surface  and  tracing  their 
intersections  with  the  surface.  The  eye  recognizes  90°  with  close 
approximation  and  fractional  parts  of  90°  such  as  45°,  30°,  60° 
with  fair  accuracy. 

Parallelism  of  faces  is  judged  by  placing  one  of  the  faces  in 
contact  with  a  horizontal  surface  and  noting  the  position  taken 
by  the  other  face.  Parallelism  between  a  face  and  a  line  is 
judged  by  placing  a  straight  edge  in  different  positions  of  contact 
with  the  face.  If  in  any  of  the  positions  the  straight  edge  and 
the  line  are  parallel,  the  face  and  the  line  are  also  parallel.  Paral- 
lelism of  three  or  more  faces  to  a  common  line  is  judged  by  the 
parallelism  of  the  edges  between  the  faces. 

The  Measuring. 

A  convenient  order  of  measuring  and  recording  is  as  follows: 
A  zone,  or  series  of  planes  parallel  to  the  same  line,  is  selected 
which  shows  numerous  or  very  well  developed  faces.  This  zone 
is  placed  with  the  faces  vertical  and  a  sketch  made  by  tracing 
(or  following  approximately)  these  faces  on  the  paper,  giving  for 
instance  the  outline  a,  b,  c,  d,  e^f,  g,  h,  Fig.  3.  The  edges  between 
the  oblique  planes  are  then  roughly  sketched  in  and  letters  or 
numbers  assigned  to  each  oblique  face. 

Each  angle  of  the  vertical  zone  is  then  measured  two  or  three 


6  CRYSTALLOGRAPHY. 

times,  taking  care  to  reset  the  goniometer  after  each  reading. 
The  average  for  each  angle  is  then  recorded.  Usually  the  supple- 
ment angle,  which  can  be  read  directly  on  Penfield  Model  B, 
is  read  and  recorded,  partly  because  the  sum  of  all  the  supplement 
angles  of  a  zone  is  360°,  partly  because  other  angles  are  more 
simply  checked  or  calculated  and  largely  because  crystallographic 
descriptions  almost  invariably  record  the  supplement  angles. 


FIG.  4. 


Any  angle  is  conveniently  designated  by  the  symbols  of  the 
two  faces,  for  instance,  the  angle  between  a  and  b  by  a  A  b,  the 
angle  between  /  and  x  by  t  A  x  and  so  on. 

If  the  crystal  is  many-faced  it  may  be  convenient  to  also  draw  a  circle  and  letting 
some  point  as  c,  Fig.  4,  represent  the  face  c,  Fig.  3,  layoff  the  supplement  angles  of 
that  zone  as  arcs  and  draw  the  corresponding  radii.  By  methods  described  later,  p. 
84,  this  drawing  may  be  made  to  include  the  oblique  faces.  One  advantage  is 
that  the  unequal  development  of  corresponding  faces  of  a  zone  makes  no  change 
in  the  position  of  the  "poles"  a,  b,  c,  etc.,  of  Fig.  4.  The  "ideal"  and  the  actual 
yield  the  same  "poles."  The  angles  between  oblique  faces  or  oblique  and  vertical 
faces  are  then  measured. 

All  essentially  equal  angles  are  assembled  and  considered. 
Necessarily  such  an  assemblage  groups  together  angles  between 
"equivalent"  faces — it  may  also  include  angles  between  non- 
equivalent  faces.  Usually  other  facts  will  quickly  separate  these. 


THE   SYMMETRY   OF   CRYSTALS. 


Although  the  angles  between  corresponding  faces  of  all  crystals 
of  the  same  substance  are  equal,  different  crystals  of  the  same 


INTR  OD  UCTOR  Y.  7 

substance  often  show  unequal  numbers  of  faces,  different  angles 
and  notably  different  shapes. 

The  property  which  such  very  different  crystals  of  the  same 
substance  have  in  common  is  expressed  by  the  following  law: 

The  Law  of  Symmetry. 

All  crystals  of  any  one  substance  are  of  the  same  grade  of  symmetry. 

Symmetry  is  fundamentally  repetition.  The  sphere  has  in- 
finite geometric  symmetry.  Every  plane  through  the  center 
divides  it  into  symmetrical  halves.  Every  diameter  is  an  axis 
of  infinite  symmetry. 

True  geometric  symmetry  to  lines  and  planes  is  rarely  shown 
in  the  shapes  of  crystals.  The  actual  symmetry  is  a  symmetry 
in  molecular  structure  (see  page  26),  a  repetition  in  different 
directions  of  exactly  the  same  arrangement.  This  shows  in  the 
crystal  shape  but  as  symmetry  of  direction  with  repetition  of 
equal  angles  and  not  often  as  symmetry  of  position  with  repetition 
of  equal-sized  faces. 

That  is,  there  is  in  practically  every  crystal  some  repetition  or 
recurrence  of  equal  angles  or  similarly  grouped  faces,  and  two 
faces  symmetrical  in  this  sense  may  be  unequally  distant  from  the 
center,  unequal  in  size  and  different  in  shape.* 

The  "  Elements  "  of  Symmetry. 

It  is  customary  to  consider  the  symmetry  of  a  crystal  with 
reference  to  the  center,  axes,  and  planes,  these  being  collectively 
known  as  "Elements  of  Symmetry." 

Symmetry  to  the  Center. 

Each  face  of  the  crystal  has  an  opposite  parallel  face.  Thus 
Fig.  5  represents  a  crystal  of  axinite  with  opposite  parallel 
faces. 

Symmetry  to  an  Axis. 

When  the  crystal  is  revolved  about  some  line  through  the 
center  each  group  of  faces  is  repeated  2,  3,  4,  or  6  times  during  the 
revolution. 

*  They  will,  however,  be  alike  in  lustre,  markings  and  angles  they  make  with 
planes  or  axes  of  symmetry. 


CR  YSTALLOGRAPHY. 


Thus  in  each  of  the  orthographic  projections,  Figs.  6,  7,  8,  9,  10, 
there  is  an  axis  of  symmetry  perpendicular  to  the  plane  of  the 
paper. 

"Axes"  of  symmetry  in  crystals  are  rather  directions  than  lines 
through  specific  points.  Thus  while  in  the  topaz  crystal  of  ideal 


FIG.  5. 


FIG.  6. 


FIG.  7. 


shape  shown*  in  Fig.  6  there  is  an  axis  of  two-fold  geometric 
symmetry  perpendicular  to  the  plane  of  the  page  and  through  the 
center  of  the  drawing,  the  topaz  crystal  of  Fig.  7  showing  the  same 
number  of  faces  at  the  same  angles  has  only  symmetry  of  direction 
to  an  axis  perpendicular  to  the  page.  Whether  the  axis  is  consid- 
ered to  be  central  or  not  is  of  no  consequence. 

Figs.  8,  9,  10  show  respectively  projections  of  calcite  with  a 
three-fold  axis,  zircon  with  a  four-fold  axis  and  beryl  with  a  two- 
fold axis.  The  axis  in  each  case  is  perpendicular  to  the  plane  of 
the  page. 

Finding  an  Axis  of  Symmetry. 

Try  any  evidently  prominent  direction,  place  it  in  a  vertical 
position.  Note  first  whether  there  are  any  recurrent  angles  in 
the  group  of  faces  (if  any)  which  are  parallel  to  it;  if  not  it 
cannot  be  an  axis  of  symmetry.  If  there  are  recurrent  angles  in 
the  zone  of  faces  parallel  to  the  direction  note  next  the  oblique 
faces  and  revolve,  or  imagine  a  revolution  of,  the  entire  crystal 
about  the  direction.  Note  the  grouping  of  faces  at  any  initial 
position.  If  during  the  revolution  new  groups  of  faces  appear  to 

*  These  drawings  6-10  are  orthographic  projections  on  a  horizontal  plane  with 
one  zone  vertical.  Parallel  edges  appear  as  parallel  lines. 


INTR  OD  UCTOR  Y.  9 

take  positions  parallel  to  the  initial  positions  of  all  the  faces  the 
direction  of  rotation  is  a  probable  axis  of  symmetry.  If,  by 
measurement,  the  angles  for  one  position  correspond  in  value  and 
order  with  those  for  the  other  position  the  existence  of  the  sym- 
metry axis  is  confirmed. 

According  to  the  number  of  times  corresponding  groups  or 
faces  recur  during  a  complete  revolution  about  a  symmetry  axis, 
the  axis  is  known  as  two-fold,  three-fold,  four-fold,  or  six-fold. 
No  other  varieties  exist. 


FIG.  8. 


FIG.  9. 


FIG.  10. 


Symmetry  to  a  Plane. 

A  plane  of  symmetry  holds  a  definite  angular  relation  to  a 
crystal  rather  than  a  fixed  position  in  the  crystal.  So  regarded 
it  may  be  said  that  with  respect  to  any  plane  of  symmetry  the 
crystal  faces  are  in  pairs  and  that  the  angle  between  each  pair  is 
bisected  by  the  plane  of  symmetry,  or  that  a  plane  of  symmetry 
is  so  related  to  a  crystal  that  on  each  side  of  that  plane  there  will 
be  grouped  the  same  number  of  faces  at  the  same  angles  to  it 
and  to  each  other  and  in  the  same  order.  Thus,  not  only  in  the 
model  illustrated,  Fig.  6,  but  in  the  crystals  shown  in  Figs.  7,  8, 
9,  10  there  are  planes  of  symmetry  parallel  to  each  of  the  dot  and 
dash  lines  and  each  perpendicular  to  the  plane  of  the  paper. 

The  Law  of  Symmetry  therefore  means : 

That  while  the  crystals  of  any  one  substance  will  not  all  be 
alike  in  shape  even  when  the  variations  due  to  size  and  to  unequal 
development  of  faces  have  been  eliminated,  there  will  be,  in  every 
crystal  of  the  substance,  wherever  found  or  under  whatever  con- 
ditions formed,  the  same  "Elements"  of  symmetry. 


10 


CR  YSTALLOGRAPHY. 


Crystal  Models  and  their  Geometric  Symmetry. 

Models  in  which  all  equivalent  faces  are  the  same  distance  from 
the  center,  and  therefore  of  equal  size  and  the  same  shape,  are 
much  used  in  crystallography.  It  is  desirable  to  restrict  this  use 
as  the  skill  acquired  in  the  study  of  models  is  of  little  use  in  the 
recognition  of  crystals.*  Fundamentally  the  problem  is  to  recog- 
nize directions  of  equivalent  structure.  In  the  crystal  such  direc- 
tions are  indicated  by  faces  symmetrical  in  direction,  alike  in 
markings,  luster  and  relation  to  cleavage  but  of  any  size  or  shape, 
while  in  the  model  such  directions  are  indicated  by  faces  sym- 
metrical in  position  and  alike  in  size  and  shape. 

A  model  is  symmetrical  to  the  center  when  every  straight  line 
through  the  center  encounters  at  equal  distances  on  each  side  of 
the  center  two  corresponding  points. 

A  model  is  symmetrical  to  an  axis  when  if  revolved  about  this 
axis  the  model  reoccupies  the  same  position  in  space,  two,  three, 
four,  or  six  times  during  one  complete  revolution.  That  is, 
corresponding  groups  of  glanes  exchange  positions  after  revolutions 
of  180°,  120°,  90°  or  60°. 


FIG.  ii. 


FIG.  12. 


FIG.  13. 


FIG.  14. 


The  line  CC  in  the  zircon  crystal,  Fig.  n,  is  an  axis  of  four-fold 
or  tetragonal  symmetry,  for,  as  shown  in  the  horizontal  projection, 
Fig.  12,  the  crystal  occupies  the  same  position  in  space  when  by 
rotation  about  CC  any  point  a  has  moved  to  b,  c,  d  or  again  to  a, 
and  does  not  for  any  other  position. 

*  Crystals  are  often  spoken  of  in  terms  of  models  and  said  to  be  "distorted" 
when  conforming  perfectly  to  all  known  crystal  laws  but  not  resembling  the  model. 


INTRODICTORY. 


II 


The  line  CC  in  the  apatite  crystal,  Fig.  13,  is  an  axis  of  six-fold 
or  hexagonal  symmetry,  because,  as  shown  in  horizontal  projection, 
Fig.  14,  the  crystal  occupies  the  same  position  in  space  when  by 
rotation  about  CC  any  point  a  has  moved  to  b,  c,  d,  e,  f  or  again 
to  a. 

A  model  is  symmetrical  to  a  plane  when  the  plane  so  divides  it 
that  either  half  is  the  mirrored  reflection  of  the  other,  and  every 
line  perpendicular  to  the  plane  connects  corresponding  parts  and 
is  bisected  by  the  plane  of  symmetry. 


FIG.  15. 


FIG.  16. 


For  example,  in  Fig.  15,  the  shaded  plane  so  divides  the  model 
that  a  line  from  an  angle  b  perpendicular  to  the  plane  passes 
through  a  corresponding  angle  a,  or  a  perpendicular  from  c,  the 
center  of  an  edge,  passes  through  d,  the  center  of  a  similar  edge. 
ab,  cd  and  all  similar  lines  are  bisected  by  the  shaded  plane. 

In  Fig.  1 6  both  of  the  shaded  planes  are  planes  of  geometric 
symmetry  for  the  model. 

Classification  of  Crystals. 

The  basis  of  classification  is  always,  directly  or  indirectly, 
symmetry  and  profound  investigations  have  proved  that  the 
crystal  structure  as  limited  by  the  law  of  simple  mathematical 
ratio  is  of  32  types  or  classes.  Nearly  all  the  important  minerals 
crystallize  in  ten  or  eleven  of  the  thirty-two  classes. 

The  six  crystal  *' systems"  constitute  a  more  convenient  classifi- 
cation. Each  system  includes  two  or  more  classes.  Two  methods 
of  determining  system  will  be  described. 


12  CRYSTALLOGRAPHY. 

1.  A  method  based  on  partial  symmetry,  which  is  very  quickly 
and  easily  used  for  determining  the  systems  of  actual  crystals 
and  which  supplemented  by  angle  measurements  will  often  deter- 
mine the  mineral. 

2.  A  method  based  on  crystal  axes,  but  indirectly  upon  sym- 
metry in  the  choice  of  crystal  axes.     This  is  indispensable  in 
a  mathematical  consideration  of  the  relations  between  faces  and 
in  the  understanding  of  a  crystal  description. 

CONSIDERATION  OF  CRYSTALS  BY  PARTIAL  SYMMETRY  AND 
APPROXIMATE   ANGLES,    WITHOUT   SYMBOLS. 

Rapid  Method  for  Finding  the  System  of  a  Crystal. 

The  following  rules  quickly  determine  the  "system"  of  a 
crystal,  without  the  need  of  a  complete  determination  of  symmetry 
or  any  consideration  of  "crystal"  axes.  They  apply  to  all  32 
classes  except  one.* 

Approximate  measurements,  as  described  p.  5,  are  usually 
needed. 

Essential  Condition.  System. 

More  than  one  axis  of  three-fold  sym-  Isometric. 

metry. 
One  axis  of  four-fold  symmetry,  and  one  Tetragonal. 

only. 
One  axis  of  three-fold  symmetry,  and  one  Hexagonal. 

only.  Rhombohedral  division. 

One  axis  of  six-fold  symmetry.  Hexagonal  division. 

More  than  one  axis  of  two-fold  symmetry  Orthorhombic. 

but  no  axis  of  higher  symmetry  (or  one 

axis  and  two  planes  of  symmetry). 
One  axis  of  two-fold  symmetry  only,  or  Monoclinic. 

one  plane  of  symmetry  only,  or  both. 
Without  axes  or  plane  of  symmetry.  Triclinic. 

DISTINGUISHING   SPECIES   BY   APPROXIMATE   ANGLES. 
Because  the  angles  between  corresponding^  faces  are  constant 
and  characteristic,  the  measuring  of  a  few  selected  angles  will 
often  serve  to  determine  the  mineral.     Certain  angles  are  char- 

*  The  scalenohedral  class  of  the  tetragonal  system  by  these  rules  would  be  ortho- 
rhombic. 

t  Corresponding  faces  on  the  same  crystal,  or  on  different  crystals  of  the  same 
substance,  occupy  corresponding  or  symmetrical  positions  with  reference  to  the 
symmetry  axes  and  usually  correspond  in  lustre  and  markings.  They  frequently 
do  not  correspond  in  shape. 


INTR  OD  UCTOR  Y. 


acteristic,  others  are  common  to  many  crystals,  for  instance,  the 
angles  between  faces  parallel  to  the  four-fold  axis  in  the  tetragonal 
are  possible  angles  for  any  substance  crystallizing  in  the  tetragonal 
system. 

The  "cleavage"  directions  are  of  great  service  in  orienting  the 
crystal.  These  and  the  angles  between  them  are  used  in  the  lists 
which  follow  each  system. 

ISOMETRIC    SYSTEM. 

Principal  Characteristic. 

If  a  crystal  has  more  than  one  axis  of  three-fold  symmetry  it 
is  an  isometric  crystal  and  not  otherwise.  It  may  or  may  not 
have  three  four-fold  axes. 

Prominent  Features. 

The  bounding  planes  are  often  squares  and  equilateral  triangles 
or  these  with  their  corners  cut  off.  Corresponding  faces  and  equal 
angles  are  more  frequent  than  in  other  systems.  Often  the  dimen- 
sions are  closely  equal  in  three  or  more  directions. 

Angles. 

These  are  of  the  same  "series"  whatever  the  species.     They 
are  therefore  classed  by  their  "habit,"  that  is,  dominant  "forms" 
on  the  crystals. 
Tetrahedral,  Fig.  17. 

(Four  faces  at  70°  31'.)     Sphalerite,  tetrahedrite. 


FIG.  17. 


FIG    18. 


FIG.  19. 


Cubic,  Fig.  1 8. 

(Six    faces    at   90°.)     Argentite,    cuprite,    fluorite,    galenite, 

halite,  pyrite,  smaltite. 
Octahedral,  Fig.  19. 

(Eight  faces  at  109°  29'.)     Chromite,  cuprite,  fluorite,  frank- 

linite,  galenite,  linnaeite,  magnetite,  pyrite,  spinel. 


CR  YSTALLOGRAPHY. 


Dodecahedral,  Fig.  20. 

(Twelve  faces  at  120°.)     Cuprite,  garnet,  magnetite,  sphaler- 
ite. 

Pyritohedral,  Fig.  21. 

(Twelve  faces  often  at   126°  53'  and   113°  35'.)     Cobaltite, 
pyrite,  smaltite. 

Trapezohedral ,  Fig.  22. 

(Twenty-four  faces  often  at  131°  19'  and  146°  27'.)     Analcite, 
garnet,  leucite. 


Fie.  20. 


FIG.  21. 


FIG.  22. 


The  following  show  notably  good  cleavages: 
Cubic.     Galenite,  halite. 
Octahedral.     Fluorite. 
Dodecahedral.     Sphalerite. 

TETRAGONAL   SYSTEM. 

Principal  Characteristic.* 

If  the  crystal  shows  one  axis  of  four-fold  symmetry  and  only 
one  it  is  a  tetragonal  crystal. 

Prominent  Features. 

A  section  taken  at  right  angles  to  the  four-fold  axis  is  usually 
square  or  octagonal,  that  is  with  angles  of  90°  or  135°  between 
adjacent  faces. 

The  dimension  in  direction  of  the  four-fold  axis  is  usually  notably 
greater  or  less  than  in  directions  at  right  angles  thereto. 

Angles. 

In  the  zone  of  the  four-fold  axis  (faces  a,  m,  Fig.  23)  there  are 
no  variations  in  angle  dependent  on  the  species.  All  show  the 
same  series  of  angles  and  between  corresponding  faces  these  are 
principally  90°,  more  rarely  143°  8'. 


INTRODUCTORY. 


In  all  other  zones  the  angles  vary  with  the  species. 
Those  important  tetragonal  minerals  which  often  show  macro- 
scopic crystals  may  be  classified  by  angles  and  cleavage  as  follows : 

ANGLES  BETWEEN  CORRESPONDING  FACES  OBLIQUE  TO  THE 
FOUR-FOLD  Axis. 

71°  20'  chalcopyrite.  121°  41'  cassiterite. 

99°  38'  wulfenite.  123°    8'  rutile  (p  A  p,  Fig.  23). 

100°    5'  scheelite.  123°  19'  zircon. 

105°        apophyllite.  129°  21'  vesuvianite. 

109°  53'  braunite.  136°  15'  wernerite. 

Braunite,  scheelite  and  wulfenite  cleave  at  the  angles  mentioned. 

Wernerite  and  rutile  cleave  parallel  the  four-fold  axis  giving 
angles  of  90°  and  135°.  Apophyllite  cleaves  to  cubic  forms,  but 
in  one  direction  much  more  easily  than  in  the  other  two. 


FIG.  23. 


FIG.  24. 


FIG.  25. 


HEXAGONAL   CRYSTALS. 

Principal  Characteristic. 

If  the  crystal  shows  one  and  only  one  axis  of  three- fold  sym- 
metry it  is  a  hexagonal  crystal,  rhombohedral  division. 

If  the  crystal  shows  one  and  only  one  axis  of  six- fold  symmetry 
it  is  a  hexagonal  crystal,  hexagonal  division. 

Prominent  Features. 

A  section  taken  at  right  angles  to  the  axis  of  three-fold  or  six- 
fold symmetry  is  usually  a  hexagon  or  twelve-sided,  that  is  with 
angles  of  120°  or  150°  or  in  some  minerals  an  equilateral  triangle 
with  the  corners  "modified." 

The   dimension   parallel   this   axis   is   usually   notably   greater 


1 6        ,  CRYSTALLOGRAPHY. 

(prismatic  crystals)  or  less  (tabular  crystals)  than  the  dimensions 
at  right  angles  thereto. 

Angles. 

In  the  zone  of  the  three-fold  axis,  Fig.  24,  or  six-fold  axis,  Fig. 
25,  there  are  no  variations  in  angle  dependent  on  the  species. 
All  show  the  same  series  of  angles  and  between  corresponding 
faces  these  are  principally  120°  or  larger  such  as  141°  47'  the  occur- 
rence of  which  tends  to  produce  a  nearly  circular  cross  section. 

In  all  other  zones  the  angles  vary  with  the  species. 

The  important  hexagonal  minerals,  which  occur  frequently  in 
macroscopic  crystals,  may  be  classified  by  angles  and  cleavage 

as  follows: 

• 

I.   WITH  Axis  OF  THREE-FOLD  SYMMETRY  (USUALLY  RHOMBOHEDRAL  HABIT). 
(a)  Angles  are  both  interfacial  and  cleavage:  (b)  Angles  interfacial  only: 

85°  14'  chabazite.  107°         rhodochrosite.  85°  31'  ilmenite. 

86°         hematite.  107°         siderite.  90°  50'  alunite. 

105°    5'  calcite.  107°  24'  magnesite.  92°  37'  willemite. 

106°  15'  dolomite.  107°  40'  smithsonite.  116°  36'  phenacite. 

107°  58'  proustite.  133°  8'    or  103°  tourmaline. 

II.   WITH  APPARENT  Axis  OF  SIX-FOLD   SYMMETRY    (USUALLY   PRISMATIC  HABIT). 
(c)  Often  capped  by  horizontal  plane:  (d)  Often  capped  by  oblique  planes: 

Beryl  nephelite.  86°    4'  or  128°    2 '  corundum. 

lodyrite  pyrargyrite.  94°  14'  or  133°  44'  quartz. 

Mimetite  pyromorphite.  142°  15'  apatite. 

Vanadinite. 

(e)   Tabular:  graphite,  molybdenite,  iridosmine. 


ORTHORHOMBIC   CRYSTALS. 

Principal  Characteristic. 

If  a  crystal  shows  either  more  than  one  axis  of  two-fold  sym- 
metry (or  one  axis  with  more  than  one  plane  of  symmetry)  and 
nothing  of  higher  symmetry  it  belongs  to  the  orthorhombic  system. 
Prominent  Features. 

Cross  sections  taken  at  right  angles  to  the  axes  of  symmetry 
are  unlike  in  angles  and  tend  to  rectangles  and  rhombs  or  these 
combined. 
Angles. 

There  is  no  zone  which  has  a  constant  series  of  angles  for  all 
species.  The  interfacial  angles  in  the  zones  parallel  to  the  axes 
of  symmetry  are  unlike  except  when  90°  and  vary  with  the  species. 


INTRODUCTORY. 


Because  the  three  axes  of  symmetry  are  all  two-fold  no  prac- 
ticable method  exists  for  distinguishing  between  them.  If,  how- 
ever, in  any  crystal  angles  are  found  that  correspond  to  important 
angles  in  the  zones  of  at  least  two  such  axes,  for  any  species,  the 
crystal  is  probably  of  that  species. 

In  the  table  the  columns  A,  B,  C  give  prominent  angles  in 
zones  parallel  to  the  three  symmetry  axes.  Other  prominent 
angles  are  assembled  in  D.  Thus  in  Fig.  26,  the  symmetry  axes 
being  shown  by  dotted  lines,  in  the  zone  of  the  vertical  axis  the 
angle  m  A  m  is  129°  31',  in  the  zone  of  the  axis  from  front  to 
back  d  A  d  is  119°  46'.  No  angles  occur  in  the  zone  of  the  axis 
from  left  to  right,  and  finally  such  an  angle  as  p  A  p  =  139° 
53'  is  evidently  prominent.  These  are  found  in  the  columns 
C,  A  and  D  respectively  under  chrysoberyl. 

The  important  orthorhombic  minerals  which  frequently  occur 
in  macroscopic  crystals  may  be  classified  as  follows: 


bisected  by  cleavage. 


t  =  parallel  cleavage. 


C 

B 

A 

D 

Stibnite 

QO°  26'  * 

108°  36' 

Andalusite 

go0  48'  t 

190°  50' 

Natrolite      ...            ... 

pz°  75' 

rare 

rare 

142°  23' 

Sillimanite  

gi°  45'  * 

none 

none 

none 

Goethite  
Enargite  
Manganite  
Brookite 

94°  52'  * 
97°  53'  t 
QQ°  40'  *  ' 
00°   ^0' 

113°    6' 

114°  19' 
rare 

117*30' 

122°  50' 

rare 

101°  31' 

Columbite 

100°  43' 

140°  37' 

06°  «?i' 

90°  f 

Barite  . 

101°  38'  t 

102°  17' 

74°  34' 

90°  t 

Sulphur  

101°  46' 

46°  i  6' 

55°  26' 

1  06°  26' 

Anglesite  
Calamine  
Celestite  
Marcasite 

103°  44'  t 
103°  51'  t 
104°  10'  t 

I0q°      q't 

101°  13' 

101°  II' 

6^°  AO' 

75°  36' 
76° 

78°      2' 

90° 
90°  t 

Arsenopyrite 

112°  27'  t 

<?6°  <?7' 

78°    5' 

Aragonite  

116°  12'  t 

108°  27' 

Cerussite  
Topaz  
Staurolite  

1/7°  14'  t 
124°  17' 
129°  20'  * 

57°  59' 
69°  28' 

108°  16' 

55°  19' 
90° 

141° 

Chrysoberyl  

129°  31' 

119°  46' 

139°  53' 

MONOCLINIC    CRYSTALS. 

Principal  Characteristic. 

If  a  crystal  shows  one  and  only  one  axis  of  two-fold  symmetry 
or  one  and  only  one  plane  of  symmetry  or  both  it  is  a  monoclinic 
crystal. 

3 


18 


CR  YSTALLOGRAPHY. 


Prominent  Features. 

Any  face  in  the  zone  of  the  symmetry  axis  makes  a  90°  angle 
with  the  symmetry  plane  (or  a  face  parallel  to  it).  No  other 
90°  angles  occur. 

The  cross  section  of  the  zone  of  the  symmetry  axis  is  never 
rhombic  or  rectangular  but  markedly  unsymmetrical. 

The  direction  of  the  symmetry  axis  is  not  usually  the  long 
dimension,  and  the  faces  parallel  to  it  are  only  alike  in  pairs. 

No  monoclinic  crystal  will  consist  of  less  than  two  kinds  of 
faces  and  there  will  never  be  more  than  four  corresponding  faces 
on  a  crystal. 


FIG.  26. 


FIG.  27. 


FIG.  28. 


Angles. 

No  zone  has  a  constant  series  of  angles  for  each  species.  The 
zone  of  the  axis  of  symmetry  can  always  be  found  and  its  angles 
measured  and  it  is  also  usually  easy  to  locate  corresponding  faces 
the  angles  between  which  are  bisected  by  the  symmetry  plane. 
These  two  sets  of  angles  have  therefore  been  used  in  the  table 
following. 

Thus  in  Fig.  27  c  A  a  =  105°  50'  is  an  angle  in  the  zone  of  the 
symmetry  axis  and  m  <  m  =  87°  10',  v  A  v  =  iu°  18'  and 
P  A  p  =  I3i°3i'are  bisected  by  the  plane  of  symmetry.  These 
are  recorded  in  the  table  as  angles  of  pyroxene. 

The  important  monoclinic  minerals  which  often  occur  in  macro- 
scopic crystals  may  be  classified  as  follows: 


INTRODUCTORY. 


Species. 

Angles  in  Zone  of 
Symmetry  Axis. 

Angles  Bisected  by 
Symmetry  Plane. 

Other  Im- 
portant 
Angles. 

Easiest  cleavage 

Colemanite 

110°     9', 

107°  56', 

*9o 

parallel  to  sym- 

III0 36' 

140°  12', 

metry  plane 

126°  9' 

Gypsum 

1^1°  "*O' 

AOA       O*-'   f 

143°  48', 

138°  40' 

Realgar 

74°  26', 

*00 

132°    3' 

yv/ 

Vivianite 

1  08°  02' 

Wolframite 

1  1  8°     6', 

100°  37', 

124°  48', 

98°    6', 

117°    6' 

i  i  7°  49' 

Easiest  cleavage 

Azurite 

135°  14', 

99°  19', 

perpendicular  to 

137°  10', 

H9°  13'. 

symmetry  plane 

132°  45' 

90°  53'. 

*59°  13' 

Borax 

106°  35' 

*87°, 

122°  33', 

96°  32' 

Epidote 

*ns°  23', 

70°    4', 

128°  19', 

70°  29', 

155°  ii' 

63°    5' 

Monazite 

140°  48', 

93°  26' 

87°  17', 

126°  29' 

Orthoclase 

99°  42', 

n8°47', 

*9o 

129°  44' 

90°    7' 

Cleavage  angle 

Amphibole 

130°    6' 

*I24°   II', 

bisected  by  plane 

148°  28' 

of  symmetry 

Pyroxene 

105°  50', 

*8?°  io', 

148°  40' 

120°  49', 

• 

131°  31' 

Spodumene 

110°  20' 

*87°, 

91°  26' 

Titanite 

140°  43', 

*H3°3i', 

159° 

136°  ii', 

67°  57' 

No  cleavage 

Datolite 

90°    9'. 

H5°  13', 

135° 

120°  56', 

115°  2l' 

The  micas  and  chlorites  are  usually  pseudohexagonal. 
TRICLINIC   SYSTEM. 

Principal  Characteristics. 

If  the  crystal  shows  neither  any  axes  nor  any  planes  of  sym 
metry  it  is  a  triclinic  crystal. 


*  =  angle  between  easy  cleavage  planes. 


20 


CR  YSTALLOGRAPHY. 


Prominent  Features. 

There  will  be  no  right  angles  either  between  faces  or  edges. 
The  only  corresponding  faces  will  be  opposite  (parallel)  faces. 

Triclinic  crystals  however  may  approximate  in  angles  mono- 
clinic  crystals  and  only  be  distinguishable  by  inspection  by  the 
occurrence  of  faces  which  have  no  symmetrically  placed  associates. 

Angles. 

All  corresponding  faces  being  parallel,  angles  between  adjacent 
faces  are  given.  Two  faces  adjacent  in  one  crystal  may  however 
be  separated  by  truncating  faces  in  another. 


Interfacial  and 
Cleavage  Angles 

Albite 93°  36' 

Anorthite 94°  10' 

Labradorite 93°  56' 

Oligoclase 93°  28' 

Amblygonite 104°  30' 

Chalcanthite 123°  10' 

Cyanite    101°  30' 

Rhodonite 87°  32' 


Angles  between  Common 
Adjacent  Faces 

127°  44',    120°  46' 

116°    3',     98°  46',   120°  31' 


128°    3', 


8',   120°  54' 


135°  30' 

110°  10',     70°  22',  103°  27' 
74°  16',   131°  42',     78°  58' 
107°  24' 


CONSIDERATION   OF   CRYSTALS    BY    CRYSTALLO GRAPHIC    AXES    AND 

SYMBOLS. 

Crystallographic  Axes. 

The  bounding  planes  or  faces  of  crystals  are  defined  in  position 
by  referring  them  to  coordinate  axes  after  the  manner  of  analytical 
geometry.  The  coordinate  axes  are  usually  (though  unfortu- 
nately) called  crystallographic  axes. 

Choosing  Crystallographic  Axes. 

It  is  always  possible  and  indeed  essential  to  choose  as  crystallo- 
graphic axes  those  lines  which  are  closely  related  to  the  symmetry 
of  the  crystal.  If  the  choice  be  made  in  the  following  order  the 
six  systems  result. 

First,  axes  of  symmetry. 

Second,  lines  perpendicular  to  planes  of  symmetry. 

Third,  lines  in  a  plane  of  symmetry  parallel  to  edges,  or  faces. 

Fourth,  lines  parallel  or  equally  inclined  to  several  faces  of  the 
crystal. 


/A 'TR  OD  UCTOR  K  21 

If  there  result  more  lines  than  are  needed,  preference  should 
be  given : 

(a)  To  directions  at  right  angles  to  each  other. 

(b)  To  interchangeable  directions,  that  is,  to  directions  such 
that  the  grouping  of  the  faces  about  one  is  the  same  as  the  grouping 
of  the  faces  about  any  other. 

The  Six  Crystal  Systems. 

The  six  systems  may  then  be  defined  in  terms  of  axes,  each 
including  all  crystals  which  are,  by  the  given  rules,  referred  to  a 
particular  set  of  axes: 

THE  TRICLINIC  SYSTEM. — Three  non-interchangeable  axes  at 
oblique  angles  to  each  other. 

THE  MONOCLINIC  SYSTEM. — Three  non-interchangeable  axes 
two  of  which  are  oblique  to  each  other,  the  third  is  at  right  angles 
to  the  other  two. 

THE  ORTHORHOMBIC  SYSTEM. — Three  axes  at  right  angles  but 
not  interchangeable. 

THE  TETRAGONAL  SYSTEM. — Three  axes  at  right  angles,  of 
which  two  are  interchangeable. 

THE  HEXAGONAL  SYSTEM. — Four  axes,  three  of  which  lie  in  one 
plane  at  sixty  degrees  to  each  other  and  are  interchangeable,  the 
fourth  is  at  right  angles  to  the  other  three. 

THE  ISOMETRIC  SYSTEM. — Three  interchangeable  axes  at  right 
angles  to  each  other. 

CRYSTAL   FACES   AND    THEIR   SYMBOLS.* 

Referring  a  Face  to  the  Crystallographic  Axes. 

Whatever  the  position  of  any  crystal  face,  CDE,  Fig.  28,  it 
must  be  either  parallel  to  or  capable  of  intersecting  each  of  the 
chosen  Crystallographic  axes. 

Its  position  in  space  is  absolutely  determined  if  the  numerical 
values  of  its  intercepts  OA,  OB  and  OC  on  the  Crystallographic 
axes  are  known. 

If  stated  as  relative  distances,  for  instance 

OA  :  OB  :  OC  =  0.7  :  I  :  1.46, 

*  The  symbols  of  Levy,  Naumann,  Dana,  Goldschmidt  are  not  used  in  this 
book.  A  description  of  these  will  be  found  in  Goldschmidt's  "Index  der  Krystall- 
foimen,"  Vol.  I. 


22  CR  YSTALL  OGRAPHY. 

these  intercepts  are  independent  of  the  absolute  position  of  the 
face  and  represent  any  face  parallel  to  it,  that  is  any  face  in  the 
same  angular  position. 

The  Miller  Indices  and  the  Weiss  Parametral  Symbols. 

Because  of  a  simple  relation  between  the  intercepts  of  different 
faces  (which  will  later  be  explained)  the  symbols  which  are  most 
used  are  not  the  relative  intercepts  of  the  corresponding  faces 
but  simpler  expressions  from  which  these  relative  intercepts  may 
be  derived. 

Parameters. 

Both  the  Miller  and  the  Weiss  symbols  require  that  the  relative 
intercepts  of  some  chosen-  face  upon  the  crystallographic  axes 
be  known.  These  particular  intercepts  are  hereafter  spoken  of  as 
Parameters.  In  Fig.  29  of  topaz  the  chosen  face  is  p  (parallel  to 
a  face  of  the  enclosed  dotted  pyramid)  and  by  calculation  the 
parameters  are  a  :  b  :  c  =  0.529  :  I  :  0.477. 

The  Miller  Indices. 

The  Miller  indices  of  any  face  are  those  numbers  which  divided 
term  by  term  into  the  parameters  give  as  quotients  the  intercepts  of  the 
face. 

Conversely  dividing  the  parameters  by  the  intercepts  will  give 
the  indices. 

The  Weiss  Coefficients. 

The  Weiss  parametral  symbols  state  the  parameter  symbol 
a  :  b  :  c  with  coefficients  and  the  Weiss  coefficients  of  any-  face 
are  those  numbers  which  multiplied  term  by  term  into  the  parameters 
give  as  products  the  intercepts  of  the  face. 

The   Miller   indices   and   the  Weiss   coefficients  are   therefore 
reciprocally  related. 
Example. 

In  crystals  of  topaz  there  occurs  a  plane  /,  Fig.  29,  for  which 
the  Miller  indices  are  (021)  and  the  Weiss  symbol  co  a  :  b  :  2c, 
but  these  symbols  alone  tell  only  that  the  face  is  parallel  the 
first  axis. 

If,  however,  the  parameters  are  known  a  :  b  :  c  =  0.529  :  i  : 
0.477,  then  it  follows  from  the  two  definitions  that  with  respect 
to  the  other  two  axes  the  intercepts  of  the  face  /  are  OB  :  OC  : 
0.5  :  0.477,  or  as  I  :  0.954. 


INTR  OD  UCTOR  Y. 


CRYSTAL   "FORMS"    OR   GROUPS    OF   EQUIVALENT   FACES. 

Crystal  faces  which  are  directions  of  identical  structure  may 
be  called  "equivalent"  faces.  Such  faces  are  sometimes  closely 
alike  in  size  and  shape.  Very  frequently  they  have  similar 
markings  and  luster  and  they  always  make  the  same  angles  with 
the  crystallographic  axes.  Their  symbols  are  therefore  variants 
of  one  symbol. 

The  crystallographic  form  in  any  symmetry  class  is  that 
assemblage  of  equivalent  faces  which  satisfies  the  symmetry  of 


FIG.  29. 


FIG.  30. 


'7'  'i 


the  class.     A  form  may  be  one  face  or  two  faces  or  as  many  as 
forty-eight  faces.     It  is  not  necessarily  a  closed  form. 
Form  Symbols. 

The  symbol  used  is  the  symbol  of  any  of  the  faces  of  the  form. 
In  the  Miller  indices,  for  instance,  {121}  signifies  a  form  to  which 
the  face  (121)  belongs,   {        }   conventionally  being  reserved  for 
forms,  (         )  for  faces. 
Combinations  of  Forms. 

A  crystal  may  be  bounded  entirely  by  faces  of  one  form.  More 
frequently  the  bounding  faces  belong  to  two  or  more  different 
forms.  Such  a  crystal  is  said  to  be  a  combination  of,  or  to  be 
composed  of,  or  to  show  such  and  such  forms,  the  symbols  being 
stated. 

If  one  of  the  forms  is  notably  more  prominent  than  the  others, 
for  instance,  the  cube,  the  crystal  is  often  described  as  a  cube 
modified  by  the  other  forms. 

Zones. 

Zones  are  composed  of  faces  all  parallel  to  the  same  line.  Their 
intersections  are  therefore  parallel  to  this  line  and  to  each  other. 


CR  YSTALL  O  GRAPH 'Y. 


It  has  sometimes  been  stated  as  a  fourth  law  of  crystals  that  the 
faces  of  crystals  tend  to  occur  in  zones.  In  the  clinographic  and 
orthographic  projections  used  in  this  book  parallel  edges  of  the 
crystal  appear  as  parallel  lines;  therefore  the  prominent  zones 
can  easily  be  traced.  For  instance,  in  Fig.  30,  m' ,  V ,  a,  /,  m,  b  are 
faces  in  one  zone,  as  are  pf,  qf ,  o,  q,  p,  or  b,  d,  e,  c  or  o',  a,  o,  c. 

THE  OCCURRENCE  OF  CRYSTAL  FACES  IN  SERIES  AS  EXPRESSED  IN 
THE  LAW  OF  SIMPLE  MATHEMATICAL  RATIO. 

A  simple  but  very  important  relation  is  found  to  exist  between 
all  true  crystal  faces  or  crystals  of  any  one  substance  which  may 
be  expressed  as  follows: 

//  the  relative  intercepts  of  all  the  faces  are  reduced  so  that  the 
same  term  in  each  is  unity,  then  in  all  crystals  of  the  same  chemical 
substance,  if  the  intercepts  of  any  face  are  divided,  term  by  term, 
by  the  corresponding  intercepts  of  any  other  face,  the  quotients  will 
be  simple  numbers  or  simple  fractions  or  infinity. 

FIG.  32. 


As  corollaries  to  this  it  follows  that  the  Miller  Indices*  and 
the  Weiss  Coefficients,  which  are  such  quotients,  must  be  simple 
numbers,  or  simple  fractions  or  infinity. 

Two  pyramids  like  those  shown  in  Fig.  31  conform  to  the  law 
and  could  occur  in  the  same  crystal  as  in  Fig.  32.  These  inter- 
cepts bear  the  following  relation: 

*  This  law  rests  on  many  thousands  of  measurements.  Its  establishment  is  due 
to  Haiiy,  for  while  de  1' Isle's  series  of  forms  (derived  by  "replacing"  the  angles  and 
other  parts  of  some  "primitive"  form  by  planes)  limited  the  angles  of  the  planes 
only  so  as  to  retain  the  symmetry  of  the  primitive  form,  Haiiy  found  he  could  build 
the  secondary  planes  by  "regular  decretions"  each  successive  layer  diminishing  by 
the  abstraction  of  one  or  more  rows  of  particles  (always  some  simple  rational  number) 
parallel  to  particular  lines.  Weiss  expressed  this  mathematical  relation  by  the  use 
of  crystal  axes  and  parameter  symbols. 


INTR  OD  UCTOR  K  25 

O4/  _  QB_'  _  06" 

04    :=  2'     0£   =     If     OC  ~  3/2' 

If  (X4,  OB  and  OC  are  taken  as  parameters  the  Miller  and  Weiss 
symbols  become: 

Miller.  Weiss 

Inner  pyramid {m}  a  :"5  :c 

Outer  pyramid (364!  20,  :  b  :  3/2  vc 

The  common  bounding  faces  almost  without  exception  have 
very  simple  indices,  usually  o,  I,  2,  3  or  4.  Somewhat  larger 
numbers  result  for  the  smaller  and  less  common  faces.  Occa- 
sionally crystal  faces  occur  for  which  indices  can  not  be  called 
simple,  such  as  (8,  14,  u)  topaz,  (n,  13,  i)  cerussite,  (3,  14,  20) 
fluorite,  (28,  7,  24)  barite. 

Such  indices  may  be  the  result  of  inaccurate  measurements  or 
of  imperfect  faces  or,  in  those  cases  in  which  the  faces  are  at  angles 
near  common  faces  (vicinal  planes),  may  be  due  to  disturbances 
or  changed  conditions  during  formation. 

THE   TYPE   FACES   IN   ANY    SYMMETRY   CLASS. 

In  each  symmetry  class  there  are  seven  typically  different 
positions  in  which  a  crystal  face  may  occur  with  respect  to  the 
chosen  crystallographic  axes. 

The  numerical  values  of  the  Miller  indices  and  of  the  Weiss 
coefficients  are  not  needed  in  the  type  symbols.  Letters,  usually 
h,  k  and  /  in  the  Miller  indices  and  m  and  n  in  the  Weiss  coefficients, 
may  be  used. 

In  the  different  classes  conventions  differ  somewhat  and  symbols 
with  them.  These  differences  are  stated  in  subsequent  chapters. 

Determination  of  Type  Symbols  by  Inspection. 

After  the  axes  have  been  chosen  and  placed  in  the  conventional 
positions  stated  under  each  system,  the  determination  of  the 
type  symbols  may  be  conducted  as  follows  in  models  and  large 
crystals. 

Place  a  straight  edge  or  pencil  in  contact  with  a  face  and, 
keeping  the  contact,  turn  the  straight  edge  until  its  relation  to 
each  axis  has  been  noted. 

First,  note  whether  the  face  is  parallel  to  any  axis.  If  the 
straight  edge  while  in  contact  with  the  face  can  be  turned  into  a 


26  CRYSTALLOGRAPHY. 

position  parallel  to  the  axis,  the  face  is  parallel  to  the  axis,  the 
corresponding  Miller  index  is  o  and  the  corresponding  Weiss 
coefficient  is  oo . 

Second,  note  whether  any  two  intercepts  of  the  face  are  equal 
in  this  case,  the  corresponding  indices  (or  the  corresponding 
coefficients)  are  then  expressed  by  the  same  letter. 

If  all  intercepts  are  unlike  all  three  letters  will  be  used,  the 
order  depending  upon  the  convention  used  in  the  symmetry  class. 
If  the  face  is  the  chosen  unit  face  the  indices  and  coefficients  will 
all  be  unity  whether  the  intercepts  are  equal  or  unequal. 

THE    CRYSTAL   STRUCTURE. 

Disregarding  the  relation  between  the  chemical  nature  of  sub- 
stances and  the  crystal  structure,*  the  geometric  forms  of  crystals 

and  many  of  their  physical  charac- 
ters prove  a  homogeneous  structure, 
in  which  each  particle  is  in  a  sim- 
ilar position  with  respect  to  those 

O 

%   surrounding  it;  each  is  the  center  of 

a  precisely  similar  group,  and  along 
any  line,  and  all  parallel  lines,  the  par- 
ticles are  equally  far  apart. 
FlG  33  Such  a  structure  is  illustrated   in 

Fig.  33,  the  particle  0  is  sur- 
rounded by  six  similar  particles  A,  B,  C,  D,  E  and  F  at  fixed 
distances  OA  =  OB,  OC  =  OD  and  OE  =  OF.  Each  of  the  six 
is  itself  the  center  of  a  similar  group,  the  intervals  in  the  same 
direction  being  as  before,  that  is  AH  =  OA,  CL  =  OC,  EK  =  OE 
and  so  on. 

Different  substances  differ  in  the  grouping  of  their  particles  so 
that  each  has  its  own  characteristic  physical  constants  and  char- 
acteristic geometric  shapes.  All  this  has  been  theoretically  con- 
sidered and  the  possible  variation  of  regular  grouping  discussed.f 
In  all  230  types  of  structure  are  recognized,  all  belonging  to 
the  32  classes  of  symmetry. 

*  Article  on  "  Crystallography,"  by  W.  J.  Pope,  Annual  Rept.  Progress  Chemistry, 
1908,  Vol.  5,  pp.  258-279. 

t  See  Report  of  Committee  "  On  Structure  of  Crystals,"  Proc.  Roy.  Soc.,  Section 
C,  Glasglow,  1091,  for  a  general  review. 


INTRODUCTORY. 


27 


The  Possible  "  Forms  "  on  Crystals  of  One  Substance. 

Experience  proves  that  well-developed  faces  upon  crystals  of 
the  same  substance  occur  at  particular  angles  dependent  upon  the 
structure  and  that  if  the  structure  is  theorized  for  a  given  substance 
(with  distances  of  particles  apart  corresponding  to  the  parameters) 
it  is  found  that  ike  net  planes  with  most  particles  lie  parallel  to  the 
bounding  faces  of  the  crystal.  To  illustrate,  let  Fig.  34  represent 
a  net  plane  through  the  crystallographic  axes  a  and  b  of  topaz 
(a  :  b  =  .5285  :  i). 

Draw  lines  connecting  B  with  consecutive  points  in  different 
directions. 

The  distances  apart  of  consecutive  points  increases  along 
different  lines  in  the  following  order: 

BA,  BD,  BE,  BF,  BG,  BH,  BK,  BL,  BM. 

* 

FIG.  34- 


The  probable  prisms  of  topaz. 

Calculating  the  angle  of  each  line  with  OD  and  comparing  with 
the  angles  of  occurring  prisms  of  topaz — 

Direction BA         BD         BE         BF         BG         BH         BK 

Calculated  angle 62°  08'  43°  25'  32°  14'  25°  19'  75°  «'  Si°  35'  82°  28' 

Face  of  topaz  corresponding  .  (no)      (120)      (130)      (140)      (210)      (230)      (410) 

That  is,  all  of  the  nine  directions  represent  actual  topaz  prisms 
and  moreover  the  most  common  of  all  are  (no)  (BA),  and  (120) 
BD,  the  directions  of  most  frequent  particles.  The  cross-section 
of  such  a  group  of  prisms  is  shown. 


28  CRYSTALLOGRAPHY. 

If  the  net  plane  through  the  axes  a  and  c  be  similarly  con- 
structed for  topaz,  with  distances  of  particles  apart  corresponding' 
to  the  parameters  a  :  c  =  0.529  :  0.477  (or  I  :  0.901),  it  would  be 
found  similarly  that  the  directions  which  passed  through  most 
points  would  correspond  to  such  forms  as  {021}  and  {041}. 

Rogers  in  a  similar  figure  shows  that  if  the  net  plane  through  two  isometric  axes 
is  considered  the  directions  with  most  frequent  points  correspond  to  forms  in  the 
following  order. 

Cube  {100},  dodecahedron  {no},  tetrahexahedrons  (or  pyritohedrons)  {210}  {310} 
{320}. 

These  constructions  for  simplicity  have  considered  only  the  re- 
lations to  two  axes  and  assumed  parallelism  to  the  third,  but  the 
i  positions  of  faces  which  intersect  all  axes  are  just  as  strictly  indi- 
cated by  a  consideration  of  the  entire  "  space  lattice." 

Form  Names. 

Two  methods  of  naming  forms  exist  both  of  which  are  based  to 
a  considerable  extent  on  the  shape  of  the  form  but  in  the  one 
some  attention  is  paid  to  the  position  of  their  faces  on  the  crystal 
and  in  the  other,  except  in  the  case  of  domes  and  sphenoids,  this 
is  disregarded.  The  latter  plan  leads  to  greater  uniformity  in 
names, f  the  former  is  in  more  general  use  and  has  been  retained 
in  this  book.  It  is  of  relatively  little  importance  what  names  are 
used,  the  forms  are  better  expressed  by  their  symbols. 

*  Introduction  to  Study  of  Minerals,  p.  73. 

t  The  type  names  by  this  method  are  "pedion"  a  single  face,  "  pinacoid  "  two 
parallel  faces,  "  dome  "  two  planes  intersecting  in  a  plane  of  symmetry,  "  sphenoid  " 
two  planes  intersecting  on  a  two  fold  axis,  "  prism  "  three  or  more  planes  with 
parallel  intersections,  "pyramids"  three  or  more  planes  intersecting  at  a  common 
point,  "  bipyramids "  two  pyramids  "base  to  base."  To  these  must  be  added 
scalenohedrons,  trapezohedrons,  rhombohedrons,  and  the  usual  names  of  the 
isometric  system. 


CHAPTER  II. 


TRICLINIC    SYSTEM.* 

THE  Triclinic  System  includes  two  classes  in  both  of  which  the 
crystallographic  axes  are  three  lines  oblique  to  each  other  and  not 
interchangeable. 

PINACOIDAL    CLASS.      2. 

No.  31.   Holohedry,  Liebisch.     No.  31.   Normal  Class,  Dana. 

Choosing  Crystallographic  Axes. 

Usually  the  intersections  of  three  prominent  faces  are  chosen  as 
axes  and  one  is  conventionally  made  the  vertical  axis  c,  the  others 
the  macro  or  b  axis  and  the  brachy  or  d  axis. 

The  Seven  Type  Forms. 

Each  form  consists  of  two  parallel  faces  as  follows  : 

i.  TETRAPYRAMID. — nd\l)\mc\   {hkl}. 

Two  parallel  faces  which  intersect  all  axes,  Fig.  35.  For  any 
set  of  intercepts  four  independent  forms  result  which  if  combined 
make  a  complete  triclinic  pyramid  as  shown  in  Fig.  36.  Fig.  43 

FIG.  35.  FIG.  36.  FIG.  37. 


shows  two  tetra-pyramids  pf  =  a  :  b  :  c  =  1 1 1   and  'p  =  a  :  b'  :  c  = 
1 1 1  of  the  mineral  axinite. 

*  Also  known  as  Tetarto  prismatic,  Ein-und-eingliedrige,  Triclinbhedral,  Clinorhom- 
boidal,  Anorthic,  Doubly  oblique  and  Asymmetric. 

29 


CR  YSTALLOGRAPHY, 


2.  HEMI  BRACHY  DOME. —  oo  a  \~b\mc\   {okl}. 

Two  faces  each  parallel  to  the  brachy  axis.     The  face  e  and  its 
opposite,  Fig.  37,  modifying  the  three  pinacoids. 

3.  HEMI  MACRO  DOME. — d\cob:mc\   {hoi}. 

Two  faces  each  parallel  to  the  macro  axis.     The  face  d  and  its 
opposite,  Fig.  38,  modifying  the  pinacoids. 

4.  HEMI  PRISM.  —  nd:b:<&c\   {hko}. 

Two  faces  each  parallel  to  the  vertical  axis.     The  face  m  and 
its  opposite,  Fig.  39,  modifying  the  pinacoids. 

5.  BASAL  PINACOID. —  co#:co£:r;  {ooi}. 

Two  faces  each  parallel  to  both  the  macro  and  brachy  axes.    The 
faces  c  in  Figs.  38  to  40. 


FIG.  38. 


FIG.  39. 


FIG.  40. 


6.  BRACHY  PINACOID. — oo<2:£:co  c\  {oio}. 

Two  faces,  each  parallel  to  the  brachy  and  vertical  axes.     The 
faces  b  of  Figs.  3  8  to  40. 

7.  MACRO  PINACOID. — £:oo£:co<r;    {100}. 

Two  faces  each  parallel  to  the  macro  and  vertical   axes.      The 
faces  a  of  Figs.  38  to  40. 
Combinations  in  the  Triclinic  System. 

Fig.  41  shows  a  crystal  of  chalcanthite  with  brachy  pinacoid  by 


FIG.  41. 


FIG.  42. 


FIG.  43. 


TRICLINIC  SYLTEM. 


macro  pinacoid  a,  right  hemi  prism  m,  left  hemi  prism  J/and  lower 
left  tetra  pyramid  'p.  Fig.  42  shows  a  crystal  of  cyanite  with  the 
three  pinacoids  a,  b  and  c,  the  right  m,  and  left  M  hemi  unit  prisms 
and  a  right  hemi  brachy  prism  /  =  (2^  :  1)  :  oo  c)  ;  {120}. 

Fig.  43  shows  a  crystal  of  axinite  with  both  hemi  prisms  m  and 
Mt  macro  pinacoid  a,  upper  right  and  upper  left  unit  pyramids  /' 
and  '/  and  a  macro  dome  e  —  (ti  :  oo  T)  :  2c)  ;  {201}. 


WEISS. 


na  :  7  :  me 


MILLER. 


Tabulation  of  the  Seven  Type  Forms 

NAME.  FACES. 

Each  face  intersects  all  axes  : 

1.  TETRA  PYRAMID,  2 
Each  face  parellel  to  one  axis  : 

2.  HEMI  BRACHY  DOME, 

3.  HEMI  MACRO  DOME, 

4.  HEMI  PRISM, 
Each  face  parallel  to  two  axes  : 

5.  BASAL  PINACOID, 

6.  BRACHY  PINACOID, 

7.  MACRO  PINACOID, 


Other  Classes  in  Triclinic  System. 

One  other  class  known  as  the  unsymmetrical  class  exists  and  in 
this  each  form  is  a  single  face.  No  examples  among  minerals  are 
known  but  among  salts  there  is  calcium  thiosulfate,  CaS2O3  •  6H2O. 


)OME,           2 

oo  a  :  b  :  me 

[okl] 

DME,               2 

a  :  oo  b  :  me 

{hoi} 

2 

na  :  b  :  oo  c 

{hko} 

KCS  \ 
2 

oo  a  :  oo  b  :  c 

{001} 

[D,                   2 

oo  a  :  b  :  oo  c 

{010} 

),                     2 

a  :  oo  If  :  oo  J 

{100} 

CHAPTER  III. 


MONOCLINIC   SYSTEM.* 

THE  monoclinic  system  includes  three  classes  of  symmetry,  in 
all  of  which  the  crystallographic  axes  may  be  chosen  so  that  two 
are  oblique  to  each  other  and  the  third  normal  to  the  other  two. 
The  axes  are  not  interchangeable. 

PRISMATIC   CLASS.     5. 

No.  28.   Holohedry,  Liebisch,     No.  28.   Normal  Group,  Dana. 


FIG.  44. 


All  the  common  monoclinic  minerals  occur 
in  crystals  symmetrical  to  one  plane  and  to 
one  axis  at  90°  to  the  plane,  Fig.  44. 
Choosing  Crystallographic  Axes. 

The  axis  of  symmetry  is  always  chosen  as 
the  axis  b  and  placed  horizontally  from  right 
to  left. 

Two  other  axes,  oblique  to  each  other,  are 
chosen  f  in  the  plane  of  symmetry  one  of 
which  is  placed  vertically  and  denoted  by  c  the 
other  a  "the  clino"  dips  downward  from  back 
to  front.  The  acute  angle  between  the  verti- 
cal and  clino  axis  is  called  /9. 
Tabulation  of  the  Seven  Type  Forms. 


NAME. 

FACES. 

WEISS. 

MILLER. 

Each  face  intersects  all  axes  : 

i.  HEMI  PYRAMID, 

4 

na\~b  \  me 

{hkl} 

Each  face  parallel  to  one  axis  : 

2.  CLINO  DOME, 

4 

coa\F\  me 

{okl} 

3.  HEMI  ORTHO  DOME, 

2 

a  :  cob  ;  me 

{ho!} 

4.  PRISM, 

4 

na\~b  \  coc 

{Mo} 

Each  face  parallel  to  two  axes  : 

5.  BASAL  PINACOID, 

2 

cod  '.  cob  '.  c 

{001} 

6.  CLINO  PINACOID, 

2 

co  a  \  b  ;  cor 

{010} 

7.  ORTHO  PINACOID, 

2 

a  \  cob  '.  coc 

{'00} 

*  Also  called  Hemiprismatic,  Zwei-und-eingliedridge,  Monoclinohedral,  Clinorhom- 
bic,  Monosymmetric. 

f  For  instance  the  intersections  of  the  pinacoids  would  determine  both  directions,  or 
the  edges  of  any  prism  and  any  clino  dome  would  determine  both  directions. 

32 


MONO  CLINIC  SYSTEM. 


33 


Description  of  the  Type  Forms. 

i .   HEMI  PYRAMID.  —  na:b:  me ;  {hkl}. 

Four  faces  each  intersecting  all  the  axes  in  distances  not  simple 
multiples  of  each  other.  Fig.  45  shows  a  negative  form  cut  off 
by  a  positive  ortho  dome  o. 

For  any  set  of  intercepts  two  independent  forms  result  which 
combined  form  a  complete  pyramid.  For  instance  the  combination 
of^,  Fig.  45,  with  the  corresponding  positive  form/  gives  Fig.  46. 


FIG.  45. 


FIG.  46. 


2.  CLINO  DOME. — coa  \b\mc\ 

Four  faces,  each  parallel  to  the  clino  axis  and  cutting  the  verti- 
cal and  ortho  axes  in  distances  not  simply  proportionate.  The 
faces  d  of  Fig.  47  combined  with  two  pinacoids. 

3.  HEMI  ORTHO  DOME. — a  :  oo  b  :  c  ;   {hoi}. 

Two  opposite  faces,  each  parallel  to  the  ortho  axis  and  cutting 
the  clino  and  vertical  axes  in  distances  not  simply  proportionate. 
The  faces  o  in  Figs.  45  and  48  are  the  positive  hemi  ortho  dome. 
Another  independent  form  exists  with  the  same  intercepts. 

FIG.  49. 


FIG.  47. 


FIG.  48. 


4.  PRISM.  —  na  :  1 :  oo  c  ; 
Four  faces,  each  parallel  to  the  vertical  axis,  and  cutting  the 
4 


34 


CR  YSTALLOGRAPHY. 


basal  axes  in  distances  not  simply  proportionate.     The  faces  m  in 
Fig.  48  and  subsequent  figures. 

5.  BASAL  PINACOID.  —  coa:co7>:c',   {ooi}. 

Two  faces,  each  parallel  to  both  basal  axes.  The  faces  c  of 
Fig.  49  and  subsequent  figures. 

6.  CLINO  PINACOID. — oo«:^:oor;   {oio}. 

Two  faces,  each  parallel  to  the  clino  and  vertical  axes.  The 
faces  b  of  Fig.  49  and  subsequent  figures. 

7.  ORTHO  PINACOID. — a :  co~b :  oo c ;   {100}. 

Two  faces,  each  parallel  to  the  ortho  and  vertical  axes.  The 
faces  a  of  Fig.  49  and  subsequent  figures. 

Combinations  in  the  Prismatic  Class. 

Pyroxene.- — Axes  a  :  ~b  :  c  ==  1.092  :  I  :  0.589;  $  —  74°  10'  9". 

Fig.  50  shows  the  three  pinacoids,  a,  b  and  c,  the  unit  prism  m, 
the  negative  unit  hemi-pyramid  p  and  the  positive  hemi-pyramid  v 
=  (a  :  1 :  2r);  {22?}.  Fig.  52  is  the  same  without  v  and  Fig.  51 
omits  also  the  basal  pinacoid  <r.  Fig.  5  3  shows  the  unit  prism  m,  the 


FIG.  50. 


FIG.  51. 


FIG.  52. 


FIG.  53. 


basal  pinacoid  c,  two  positive  hemi-pyramids  v  and  w  =  (a  :  b  : 
{33!};  and  a  clino  dome  z  =  (az  a  \b  \  2c)\   {021}. 


AMPHIBOLE. — Axes  a  : 
FIG.  54. 


^  =  0.551:  i  10.293;  /3=73°  58' 4". 
FIG.  55.  FIG.  56. 


MONO  CLINIC  SYSTEM. 


35 


Fig.  54  shows  the  unit  prism  m,  the  basal  and  clino  pinacoids,  c 
and  b  and  the  positive  unit  hemi  pyramid  /.  Fig.  5  5  shows  the 
unit  prism,  clino  pinacoid  and  unit  clino  dome  d  =  (oo  a  \1)  :  c). 
{oil}.  Fig.  56  shows  the  same  except  that  the  clino  pinacoid  b 
is  replaced  by  the  ortho  pinacoid  a. 

FIG.  57.  FIG.  58.  FIG.  59.  FIG.  60. 


<^> 


56' 


ORTHOCLASE.  —  Axes  a:  b:  c  =  0.658  :   1:0.555;  /3  = 
46". 

Fig.  57  shows  the  unit  prism  m,  clino  and  basal  pinacoids  fr 
and  <:,  and  positive  hemi  orthodome  y  =  (a  :  co£  :  2^:);  {20!}.  In 
Fig-  58  y  is  replaced  by  o  =  (a  :  oo  ^  :  c)  ;  {  iol}  and  in  Fig.  60 
the  clino  pinacoid  is  omitted.  Fig.  59  includes  the  forms  of  57 
and  also  a  clino  prism  2—  ($a  :~b:  coc)  ;  {130}  and  the  unit 
pyramid  p. 


Other  Classes  in  the  Monoclinic  System. 

Two  other  classes  are  known : 

3.  CLASS  OF  THE  MONOCLINIC  SPHENOID.     With  one  axis  of 
2-fold  symmetry. 

Example :    Fichtelite,   C18H32.      Examples   in   salts  are  tartaric 
acid  and  cane-sugar,  C12H22OU. 

4.  CLASS    OF   THE    MONOCLINIC    DOME.     With    one   plane    of 
symmetry. 

Examples  :  The  rare  minerals  clinohedrite  and  scolecite. 


CHAPTER   IV. 


ORTHORHOMBIC   SYSTEM. 

THE  orthorhombic  *  system  includes  three  classes  of  symmetry, 
in  all  of  which  the  crystallographic  axes  may  be  chosen  at  right 
angles  to  each  other,  but  are  not  interchangeable. 

In  this  system  of  moderate  symmetry  certain  facts  common  to 
all  crystals  can  be  better  illustrated  and  understood  than  in  the 
other  systems.  Two  of  these  are  discussed  under  the  headings 
"  Series  "  and  "  Symbols  for  Individual  Faces." 

Series. 

All  forms  which  ever  appear  upon  crystals  of  the  same  sub- 
stance belong  to  one  series.  That  is,  their  faces  occur  at  such 
angles  that  if  one  of  the  faces  is  taken  as  the  unit  and  its  intercepts 
expressed  by  d  :  b  :  c  all  other  faces  may  be  simply  expressed  in 
terms  of  this  face.  For  instance  in  the  crystals  of  topaz,  Figs.  78 
to  80,  the  calculated  intercepts  for  certain  faces  and  their  symbols, 
when  /  is  taken  as  the  unit  face,  are  as  follows  : 


FACE. 
P 


m 
I 

f 
h 


CALCULATED  INTERCEPTS. 


SYMBOLS  IN  TERMS  OF  /. 


0.528 
0.528 
0.528 
0.528 
1.056 

00 


10.477 
10.318 

:  0.954 

;  03 
:  co 
:  0.954 


0.528  :co  :  0318 


a 

1 

(T 

{in} 

a 

~b 

^3<r 

{223} 

a 

1, 

2  C 

{221} 

a 

~b 

co  c 

{HO} 

2a 

~b 

azC 

{120} 

cod 

~b 

2c 

{021} 

a 

co  b 

•  y^ 

{203} 

Symbols  for  Individual  Faces. 

For  correct  projection  and  for  use  in  calculation  face  symbols 
are  needed  which  show  the  particular  angle  in  which  the  face 
occurs.  These  are  simply  obtained  by  considering  positive  and 
negative  directions  upon  the  crystal  as  in  the  figure.  Then  the 
different  faces  of  Fig.  6 1 ,  for  which  the  form  symbol  is  n&  :  b  :  me 
or  {hkl},  have  their  individual  symbols,  (hkl\  (hkl\  (hkl\  (hk7\ 
the  minus  signs  indicating  the  negative  direction  and  the  paren- 

*  Also  called  Prismatic,  Rhombic,  Ein-und-einaxige,  Anisometric  and  Trimetric. 

36 


ORTHORHOMBIC  SYSTEM. 


37. 


theses  (  )  typifying  a  face  as  opposed  to  {  }  for  a  form.  Or  in 
Weiss' s  Symbols  the  equivalents  may  be  obtained  either  by  use  of 
minus  signs  or  a  (')  prime  upon  the  negative  intercept  thus  the 
equivalent  for  (Jikl )  would  nd :  bf :  me. 

PYRAMIDAL   CLASS.     8. 

No.  25.      Holohedry,  Liebisch.     No.  25.      Normal  Group,  Dana. 

Almost  all  orthorhombic  minerals  crystallize  in  forms  sym- 
metrical to  three  planes  at  right  angles  to  each  other,  as  in  Fig. 
62,  the  intersections  of  these  being  axes  of  two-fold  symmetry. 

FIG.  61.  FIG.  62. 


Choosing  Crystallographic  Axes. 

The  axes  of  symmetry  are  the  Crystallographic  axes.  One,  c,  is 
placed  vertically.  Of  the  two  others  the  one  on  which  the  inter- 
cept of  the  chosen  unit  face  is  the  longer,  is  placed  from  left  to 
right,  and  called  the  macro  or  b  axis  ;  the  other  axis,  placed  from 
front  to  back,  is  called  the  brachy  or  a  axis. 

The  unit  face  chosen  will  if  possible  be  a  face  of  frequent  occurrence  which  inter- 
sects all  the  axes,  or  on  account  of  similarity  of  crystals  to  some  species  of  related  com- 
position, another  choice  may  be  made  or  the  values  d,  b  and  c  may  result  from  two  dif- 
ferent faces  or  from  cleavages. 

Tabulation  of  the  Seven  Type  Forms. 

NAME.  FACES.           WEISS.           MILLER. 
Each  face  intersects  all  axes  : 

1.  RHOMBIC  PYRAMID.  8            na  \~b\mc            hkl} 
Each  face  parallel  to  one  axis  : 

2.  BRACHY  DOME.  4             cod:l>:mc           [okl] 

3.  MACRO  DOME.  4            a:  cob -.me          {hoi} 

4.  RHOMBIC  PRISM.  4            nd:~b:cDC           {hko} 


CR  YSTALLOGRAPHY. 


NAME.  FACES.  WEISS.  MILLER, 
Each  face  parallel  to  two  axes  : 

5.  BASAL  PINACOID.                2  md-.aib-.c  {001} 

6.  BRACHY  PINACOID.              2  ma:~b:cQC  {010} 

7.  MACRO  PINACOID.               2  a:  ml:  me  {100} 

Description  of  the  Type  Forms. 

I.   RHOMBIC  PYRAMID. —  na  \b  :  mc\   {hkl}. 

Eight  faces,  each  of  which  cuts  file  three  axes  in  the  same  relative 
distances,  which  are  never  simple  multiples  of  each  other.  In  the 
ideal  forms  the  faces  are  equal  scalene  triangles. 

A  pyramid  may  be  composed  either  of  faces  with  the  unit  inter- 
cepts, or  the  faces  may  be  at  other  angles,  with  any  one  or  two 
of  the  intercepts  simple  multiples  of  the  unit  intercepts. 

For  instance  if  in  the  series  of  figures  63  to  67  the  faces  /  con- 
stitute the  unit  pyramid  d  :  b  :  c  ;  { 1 1 1 }  ;  then  a  series  of  pyramids 
which  might  occur  with  this  would  have  different  symbols  and 
names.  The  pyramid  s,  shown  in  Fig.  63  enclosing  p  and  in  Fig. 


FIG.  63. 


FIG.  64. 


FIG.  65. 


FIG.  66. 


FIG.  67. 


64  combined  with  p  ;  would  be  called  a  brachy  pyramid,  its  symbol 
being  za  :  ~b  :  \c ;   {364}. 


ORTHORHOMBIC  SYSTEM. 


39 


The  pyramid  w  shown  in  Fig.  65  enclosing  /  and  in  Fig.  66 
combined  with  /  would  be  called  a  macro  pyramid,  its  symbol  be- 
ing d  :  |£ :  |<; ;  {322}  ;  and  the  pyramid  r  shown  in  Fig.  67  com- 
bined with  p  would  be  called  a  unit  series  pyramid,  its  symbol  be- 
ing d  :  b  :  2c  ;  {221}. 

2.  BRACHY  DOME. — &>a\b\mc\   {okl}. 

Four  faces,  each  parallel  to  the  brachy  axis  but  cutting  the 
macro  axis  and  vertical  axis  in  distances  not  simply  proportionate. 
The  faces  d  in  Fig.  68. 

3.  MACRO  DOME. — a\<x>!)\mc\   {hoi}. 

Four  faces,  each  parallel  to  the  macro  axis  but  cutting  the 
brachy  axis  and  the  vertical  axis  in  distances  not  simply  propor- 
tionate. The  faces  o  in  Fig.  69. 

FIG.  68.  FIG.  69. 


4.   RHOMBIC  PRISM.  —  na\b\zac  \   {hko} . 

Four  faces,  each   parallel   to   the  vertical  axis  and  cutting  the 
basal  axes  in  distances  not  simply  proportionate. 

The  intercepts  on  the  basal  axes  may  be  in  the  unit  ratio  or 


FIG.  70. 


FIG.  71. 


one  of  the   intercepts  may  be  relatively  lengthened  just  as  in  the 
pyramids. 

The  faces  m  in  Fig.  68.  In  Fig.  70  if  /  is  the  unit  pyramid 
then,  relatively,  m  is  the  unit  prism  d\b\v>c\  {no};  and  /  is  a 
brachy  prism  2d  :  b  :  oo  c ;  { 1 20} . 


CR  YSTALLOGRAPHY. 


5.  BASAL  PINACOID. — oo<#:co£:r;   {001}. 

Two  faces,  each  parallel  to  the  basal  axes.     The  faces  c  in  Figs. 
71-80. 

6.  BRACHY  PINACOID.  —  oo£:^:co<r;   {oio}. 

Two  faces,  each  parallel  to  the  brachy  and  vertical  axes.     The 
faces  b  in  Figs.  69  and  71. 

7.  MACRO  PINACOID. — ^:oo^:oor;    {100}. 

Two  faces,  each  parallel  to  the  macro  and  vertical  axes.     The 
faces  a  in  Fig.  7 1 . 
Combinations  in  the  Pyramidal  Class. 

Barite.  — Axes  a  :  b  :  c  =  0.8 1 5  :  i :  i .3 1 3. 

The  prevailing  faces  are  the  unit  prism  m,  the  basal  pinacoid  c, 
the  macro  dome  n  ==  (d  :  oo  b :  \c) ;  { 102}  ;  and  the  brachy  dome  d  = 
b'.c)-    {oil}. 

FIG.  72.  FIG.  73.  FIG.  74. 


FIG.  75. 


FIG.  76. 


FIG.  77. 


-r- 


All  of  these  are  shown  in  Fig.  77.  Fig.  76  contains  also  the 
brachy  pinacoid  b  and  Fig.  74  the  macro  pinacoid  a.  Figs.  72,  73 
and  75  are  simpler  combinations  of  the  same  forms. 

Topaz.  —  Axes  a  :  b  \c  =  0.528  :  i :  0.477. 

FIG.  78.  FIG.  79.  FIG.  80. 


Fig.  78  shows  the  unit  pyramid  p,  unit  prism  m,  brachy  prism 
l=(2a:6:coc') ;    {120};   and  the  brachy  dome  /=(co<2:  J:  2r) ; 


ORTHORHOMBIC  SYSTEM.  41 

{02 1 } .  Fig.  79  shows  the  same  forms  with  the  basal  pinacoid  c 
and  Fig.  80  shows  all  of  79  and  also  two  other  pyramids  i=(a\b\ 
\c)\  {223};  q=(a\b\2c)\  {221};  and  two  macro-domes  ^  = 
(£:  co  £:£<:);  {203} ;  and  k=  (a  :  oo  ~b  :  2c)\  {201}. 


OTHER   CLASSES   OF   THE   ORTHORHOMBIC   SYSTEM. 

6.  CLASS  OF  THE  RHOMBIC  SPHENOID.  — With  three  axes  of  two- 
fold symmetry  at  90°  to  each  other.      Examples  —  Epsomite  and 
goslarite. 

7.  HEMIMORPHIC  CLASS. — With  two  planes  of  symmetry  at  90° 
to  each  other,  intersecting  in  an  axis  of  two-fold  symmetry.      Ex- 
amples— Calamine,  stephanite  and  prehnite. 


CHAPTER  V. 
TETRAGONAL  SYSTEM.* 

IN  all  tetragonal  forms  the  crystallographic  axes  can  be 
chosen  at  right  angles  to  each  other  and  so  that  two  will  be  inter- 
changeable, that  is  will  be  surrounded  by  exactly  the  same  number 
of  faces  and  with  corresponding  faces  at  the  same  angles.  The 
grouping  of  faces  about  the  third  axis  will  not  be  the  same  as  to 
angles  and  not  necessarily  the  same  as  to  number  of  faces. 
Series. 

A  substance  can  only  occur  in  forms  of  one  class  and  in  forms 
of  one  series  in  that  class. 

Because  of  the  two  interchangeable  axes  the  intercepts  of  any 
face  upon  these  will  be  simple  multiples  of  each  other.  The  inter- 
cept upon  the  vertical  axis  will  bear  no  simple  relation  to  these  but 
when  two  different  faces  are  compared  there  will  be  found  a  simple 
relation  between  the  corresponding  intercepts  of  all  three  axes. 

Thus  for  zircon  the  common  forms  are/,  m,  u  and  x  of  Figs.  89  to  92.  For  these 
the  intercepts  and  the  symbols,  if/  be  taken  as  the  unit,  are  : 

p  I  :  I  :  0.64  =  ^  :  a  :  c  ;        I111} 

m  I  :  I  :  oo      =  a  '.a  '.  CQ  c  \  {IIQ} 

u  i  :i  :i.92  =  a:a:3c;      {331} 

x  I  :3:i.92  =  «:ja:j^;    {311} 

CLASS   OF   THE   DITETRAGONAL   PYRAMID.     15. 

No.  1 8.     Holohedry,  Liebisch.     No.  6.     Normal,  Dana. 

Symmetry  of  the  Class. 

Forms  in  this  class  are  symmetrical  to  one  conventionally  hori- 
zontal plane  and  to  four  vertical  planes  at  forty-five  degrees  to  each 
other,  Fig.  81.  The  intersections  of  these  planes  with  each  other 
are  axes  of  symmetry  and  of  these  CC  is  an  axis  of  fourfold 
symmetry. 

*  Also  called  Pyramidal,  Viergliedrige,  Zwei-und-einaxige,  Monodimetric,  Quadratic 
and  Dimetric. 

42 


TETRAGONAL  SYSTEM. 


43 


Choosing  Crystallographic  Axes. 

The  axis  of  fourfold  symmetry  is  chosen  as  the  vertical  axis 
'c  and  either  pair  of  alternate  horizontal  axes  as  the  interchange- 
able axes  a.  Let  h  be  the  index  on  the  axis  with  the  shortest 
intercept. 


FIG.  81. 


FIG.  82. 


Tabulation  of  the  Seven  Type  Forms. 


NAME. 
Each  face  oblique  to  c. 

1.  DlTETRAGONAL  PYRAMID. 

2.  PYRAMID  OF  SECOND  ORDER. 

3.  PYRAMID  OF  FIRST  ORDER. 
Each  face  horizontal. 

4.  BASAL  PINACOID. 
Each  face  vertical. 

5.  DlTETRAGONAL  PRISM. 

6.  PRISM  OF  SECOND  ORDER. 

7.  PRISM  OF  FIRST  ORDER. 


FACES.      WEISS.        MILLER. 


na  :  me 
co  a  :  me 
a  :  me 


oo  a  :  co  a  :  c 


na  :  co  e 
:  co  a  :  co  c 
a  '.  co  c 


{hkl} 
{hol} 
{hhl} 

{001} 

{hko} 

{100} 

{no} 


Description  of  the  Type  Forms. 

1.  DlTETRAGONAL    PYRAMID.  -  a  \  HO,  \  1HC  '      {kkl}. 

Sixteen  faces,  Fig.  82,  each  cutting  the  two  basal  axes  at  un- 
equal but  simply  proportionate  distances,  and  the  vertical  axis  at  a 
distance  not  simply  proportionate  to  the  other  distances.  In  the 
ideal  forms  the  faces  are  scalene  triangles. 

2.  PYRAMID  OF  SECOND  ORDER.  —  a:  co  a  :  mc\   {hoi}. 

Eight  faces,  Fig.  84,  each  parallel  to  one  horizontal  axis,  and 
cutting  the  other  and  the  vertical  axis  at  distances  not  simple 
multiples  of  each  other.  In  ideal  forms  the  faces  are  isosceles 
triangles. 

3.  PYRAMID  OF  FIRST  ORDER.  —  a  :  a  :  me  ;   {hhl}. 

Eight  faces,  Fig.  83,  each  cutting  the  horizontal  axes  at  equal 
distances,  and  the  vertical  axis  at  a  distance  not  a  simple  multiple 


44 


CR  YSTALLOGRAPHY. 


of  the  basal   intercepts.      In  ideal  forms   the  faces   are   isosceles 
triangles. 

Although  there  is  an  arbitrary  choice  of  axes  which  determines  the  order  of  the  pyra- 
mid, yet  a  first  order  unit  a  :  a  :  c  {i  1 1}  has  not  the  same  angles  as  a  second  order  unit 
a  :  co  a  :  c  {101}.  For  instance  Figs.  83  and  84  represent  these  for  the  mineral  scheelite 
and  Fig.  85  shows  the  same  forms  combined,  but  the  supplement  angle pp?  —  79°  55^' 
whereas  dd'  =  72°  40^. 

FIG.  83.  FIG.  84.  FIG.  85. 


4.  BASAL  PINACOID.  —  oo  a  :  co  a  :  c\   {ooi}. 
Two  faces,  each  parallel  to  both  the  horizontal  axes.     The  faces 
c  of  Figs.  86  to  88. 

FIG.  86.  FIG.  87.  .       FIG.  88. 


\ 


\ 


^ ''A 


5.  DlTETRAGONAL  PRISM. d  \  11(1  \  CO  C  \ 

Eight  faces,  each  parallel  to  the  vertical  axis  and  cutting  the 
two  basal  axes  in  distances  unequal  but  simply  proportionate. 
The  faces  s,  Fig.  86. 

The  adjacent  interfacial  angles  can  not  be  equal,  for  then  the  symbol  would  be 
a  :  2.4142  a  :  oo  c  which  is  opposed  to  the  law  of  rational  intercepts  (Cotangent  22°  ytf 
=  2.414213). 

6.  PRISM  OF  SECOND  ORDER.  —  a  :  co  a  :  co  c\   { 100}. 

Four  faces  each  parallel  to  the  vertical  axis  and  to  one  basal 
axis.  The  interfacial  angles  are  90°.  The  faces  a,  Figs.  87,  90, 
94,  etc. 


TETRAGONAL   SYSTEM. 


45 


7.   PRISM  OF  FIRST  ORDER.  —  a:a:coc;   {no}. 

Four  faces,  each  parallel  tc  the  vertical  axis  and  cutting  the 
basal  axes   at  equal   distances  from   the   center.     The  interfacial 
angles  are  90°.     The  faces  m,  Figs.  88,  89,  90,  etc. 
Series  and  Combinations  in  the  Class  of  Ditetragonal  Pyramid. 

By  considering  the  forms  of  each  substance  separately,  a  clear 
idea  is  obtained  as  to  the  pyramidal  forms,  which  vary  in  shape 
and  angle  with  the  relative  lengths  of  me  and  a,  although  as  ex- 


FIG.  89. 


FIG.  90. 


FIG.  91. 


FIG.  92. 


plained,  p.  36,  the  pyramids  which  occur  upon  crystals  of  any  one 
substance  are  definitely  related  in  axial  intercepts  and  usually  very 
limited  in  number. 

Zircon. — Axes  a  :  c  =  i  :  0.640. 

Fig.  89  shows  the  common  association  of  unit  pyramid  p  and 
unit  prism  m.  In  Fig.  90  these  two  forms  are  combined  with  the 
prism  of  the  second  order  a  and  in  Fig.  9 1  with  the  pyramid  u  == 
(aiai$c)\  {331}.  Fig.  92  shows  the  union  of  second  order  prism, 
unit  pyramid  and  ditetragonal  pyramid  x  =  (a  :  30  :  $c) ;  {311}. 


FIG.  94. 


FIG.  95. 


Vesuvianite.  —  Axes  a  :  c  =  I  :  0.537. 

The  unit  pyramid  in  vesuvianite  is  only  a  little  flatter  than  in 
zircon,  hence  there  is  little  difference  between  the  pyramid  angles 


46 


CR  YSTALL  OGRAPHY. 


in   Fig.  89  and  Fig.  95.     The  relative  development  of  faces,  or 
"  crystal  habit,"  is,  however,  markedly  different. 

Fig.  93  shows  the  combination  of  unit  pyramid  /,  unit  prism  m 
and  basal  pinacoid  c,  Fig.  94  shows  these  three  forms  combined 
with  the  prism  of  the  second  order  a  and  Fig.  95  shows  the  two 
prisms  and  the  unit  pyramid. 


FIG.  96. 


FIG.  98. 


FIG.  99. 


FIG.  97. 


k     A 


Apophyllite. — Axes  a  :  c  =  i  :  1.252. 

As  indicated  by  the  ratios  of  a  to  c  the  unit  pyramid  of  this 
mineral  is  much  more  acute  than  in  zircon  and  vesuvianite,  this  is 
clearly  apparent  in  Fig.  99.  The  figures  also  illustrate  well  the 
possibility  of  great  differences  in  habit  without  any  difference  in 
occurring  forms,  thus  Figs.  96,  97  and  98  are  all  combinations 


FIG.  100. 


FIG.  101. 


the  unit  pyramid  /,  basal  pinacoid  c  and  second  order  prism  a 
In  Fig.  99  the  basal  pinacoid  does  not  occur. 

Cassiterite.  — Axes  a  :  c  =  i  :  0.6723. 

In  this  the  ratio  of  a  to  c  is  closely  as  in  zircon  but  the  common 


TETRAGONAL   SYSTEM.  47 


association  is  now  the  unit  pyramid  p  with  the  second  order  pyra- 
mid d  as  shown  in  Fig.  100. 

In  Fig.  101  these  forms  occur  with  a  ditetragonal  pyramid  z  = 
(a  :  f  #  :  3<r)  {321}  and  the  unit  prism  m. 


OTHER  CLASSES  OF  SYMMETRY  IN  THE  TETRAGONAL  SYSTEM. 

Six  other  classes  of  symmetry  have  been  distinguished  in  the 
Tetragonal  system  : 

9.  CLASS  OF  THE  THIRD  ORDER  BISPHENOID.  —  With  one  axis 
of  two-fold  symmetry.     No  examples  are  known. 

10.  CLASS  OF  THE  HEMIMORPHIC  PYRAMID  OF  THIRD  ORDER. — 
With  one  axis  of  four-fold  symmetry.     Example  —  Wulfenite. 

11.  SCALENOHEDRAL  CLASS. — With  two  planes  of  symmetry  at 
90°  intersecting  in  an  axis  of  two-fold  symmetry.     Also  two  axes 
of  two-fold  symmetry  midway  between  the  planes.     Examples  — 
Chalcopyrite  and  stannite. 

1 2.  TRAPEZOHEDRAL  CLASS.  —  Without  planes  of  symmetry,  but 
with  one  four-fold  axis  at  90°  to  four  two-fold  axes.      No  exam- 
ples amoi;\g  minerals  are  known,  the  type  salt  is  nickel  sulphate, 
NiSO4-6H2O. 

13.  CLASS  OF  THE  TETRAGONAL  PYRAMID  OF  THIRD  ORDER. — 
With  one  horizontal  plane  of  symmetry  and  one  vertical  axis  of 
four-fold  symmetry.      Examples  —  Scheelite,  wernerite  and  stolzite. 

14.  HEMIMORPHIC  CLASS. — With  four  planes  of  symmetry  inter- 
secting in  an  axis  of  four-fold  symmetry.     No  examples  among 
minerals   are    known.     Examples    in    salts   are    lodosuccinimid, 
C4H4O2NI,  and  Hydrous  Silver  Fluoride,  AgFH2O. 


CHAPTER   VI. 


HEXAGONAL  SYSTEM.* 

ALL  hexagonal  crystals  are  conveniently  referred  to  four  crys- 
tallographic  axes,  one  vertical  and  at  right  angles  to  the  others, 
three  horizontal  and  interchangeable  and  at  sixty  degrees  to  each 
other. 

Bravais  proved  that  if  the  horizontal  axes  were  considered  in 
the  order  shown  in  Fig.  102,  the  indices  for  any  face  with  respect 
to  these  axes  were  always  such  that  any  one  was  equal  to  the  sum 
of  the  other  two  with  its  sign  reversed.  It  is  therefore  easiest  to 
note  the  indices  with  respect  to  the  first  two  axes  and  add  these 
and  change  the  sign  for  the  third. 

For  type  symbols  reserve  /  4wMi«  vertical  axis  and  use  h  for 
axis  with  shorter  intercept. 

RHOMBOHEDRAL   DIVISION,   SCALENOHEDRAL    CLASS. 

No.  13.   Rhombohedral  Hemihedry,  Liebisch.     No.  19.   Rhombohedral  Group,  Dana. 

This  most  important  group  in  the  hexagonal  system  includes 
the  crystals  of  such  minerals  as  calcite,  corundum,  hematite  and 
chabazite.  All  crystals  in  the  class  are  symmetrical  to  three  planes 


FIG.  102. 


FIG.  103. 


FIG.  104. 


at  60°  to  each  other.     Their  intersection  is  the  three-fold  axis 
and  there  are  three  two-fold  axes  diagonal  to  the  planes. 


*  Also  called  Rhombohedral,  Sechsgliedrige,  Drei-und-Einaxige  and  Monotrimetric. 

48 


HEXAGONAL  SYSTEM. 


49 


Choosing  Crystallographic  Axes. 

The  axes  of  symmetry  are  chosen.     The  three-fold  axis  is  the 
vertical  c,  the  others  are  horizontal  and  one  of  them  a2,  Fig.  102,  is 
placed  from  left  to  right,  and  one  a3  is  considered  to  be  negative 
in  front,  positive  behind. 
Tabulation  of  the  Seven  Type  Forms. 

FACES.          WEISS. 


NAME. 
Each  face  oblique  to  c. 

1.  SCALENOHEDRON.  12 

2.  HEXAG.  PYRAMID  2°  ORDER.        12 

3.  RHOMBOHEDRON  i°  ORDER.  6 
Each  face  perpendicular  to  c. 

4.  BASAL  PINACOID.  2 
Each  face  parallel  to  c. 

5.  DlHEXAGONAL   PRISM.  12 

6.  HEXAG.  PRISM  2°  ORDER.  6 

7.  HEXAG.  PRISM  i°  ORDER.  6 


MILLER. 

{hkll} 

{h  •  h  •  2h  • 


a  :  na  :pa  :  me 
2a  :  2a  :  a  :  me 
a  :  co  a  :  a  :  me 


oo  a  :  oo  a  :  co  a  :  c      {oooi } 


a  :  na  :  pa  \ 
2a  :  2a  :  a  : 
a  :  co  a  :  a 


CO    C 

CO   C 

co  r 


{1120} 

{1010} 


Description  of  the  Type  Forms. 

1.  SCALENOHEDRON.  —  a  \na\pa*  \mc\   {hkll} . 

Twelve  faces,  each  cutting  all  the  axes.  In  the  ideal  form  the 
faces  are  scalene  triangles.  The  adjacent  polar  edges  are  neces- 
sarily unequal. 

Fig.  103.     Also  the'faces  v,  Figs.  113  and  116. 

2.  HEXAGONAL  PYRAMID  OF  SECOND  ORDER.  —  2a\  2a:a:mc] 
\h-h-2h-l}. 

Twelve  faces,  Fig.  104,  each  cutting  one  horizontal  axis  at  a 
certain  distance,  the  others  at  twice  f  that  distance,  and  the  vertical 


FIG.  105. 


axis  at  some  distance  not  simply  proportionate 
to  the  rest.  In  the  ideal  form  the  faces  are 
isosceles  triangles. 

3.  RHOMBOHEDRON    OF    FIRST    ORDER.  —  a: 
co  a  :  a  :  me ;   [kohl] . 

Six  faces,  each  cutting  two  basal  axes  at  equal 
distances,  parallel  to  the  third  and  cutting   the 
vertical.     In  the  ideal. forms  the  faces  are  rhombs,  Figs.  105,  109, 
1 10  and  1 14. 

4.  BASAL  PINACOID.  —  co  a:  oo  a:  co  a\c  ;    {oooi }. 

Two  faces  each  parallel  to  the  three  horizontal  axes.     The  faces 
c  of  Figs.  1 06  to  1 08. 

*  It  may  be  shown  that  in  the  Weiss  symbols  the  numerical  value  of/  —  n/n( —  l) 
and  in  the  Miller  symbols  that  i  =  —  (h  -f  k) . 

f  Easily  shown  by  the  angles  in  a  horizontal  section. 

5 


CR  YSTALLOGRAPHY. 


5.  DlHEXAGONAL  PRISM. a  \  Hd  \  pa  \  CO  C  J 

Twelve  faces  each  parallel  to  the  vertical  axis  and  cutting  all  hori- 
zontal axes  at  unequal  distances,  simple  multiples  of  each  other, 
Fig.  1 06,  shows  s  =  (a  :  |#  :  ^a  :  coc);  {2130}. 

6.  HEXAGONAL   PRISM   OF  SECOND   ORDER.  —  2a  :  2a  :  a  :coc ; 
{i  120}. 

Six  faces  each  parallel  the  vertical  axis  and  cutting  one  horizontal 

FIG.  106.  FIG.  107.  FIG.  108. 


The 


axis  at  a  certain  distance,  the  other  two  at  twice  that  distance, 
faces  a,  Figs.  107  and  121. 

7.  HEXAGONAL  PRISM  OF  FIRST  ORDER.  —  a  :  co  a  :  a  :  co  c ; 
{1010}. 

Six  faces  each  parallel  to  the  vertical  and  one  horizontal  axis  and 
cutting  the  other  two  at  equal  distances.     The  faces  m,  Figs.  108, 
112  and  115. 
Combinations  in  the  Scalenohedral  Class. 

Calcite.  —  Axes  a  :  c  =  I  :  0.854. 

Figs.  109  to  116  represent  the  more  common  of  the  extremely 
numerous  forms  of  calcite.  Rhombohedrons  and  scalenohedrons 
predominate.  The  rhombohedrons  shown  are  p  the  unit,  Fig. 
109,  e  the  negative  form  of  a  :  coa  :  a  :  ±c  ;  { 1012}  ;  Fig.  1 10  ;  / 
the  negative  form  of  a  :  CD  a  :  a  :  2c ;  {2021},  Fig.  114;  and  q 
the  positive  form  of  a:  oo  a:  a  :  1 6c  ;  {16.0.16.1};  Fig.  in. 

Two  scalenohedrons  only  are  shown,  v  —  (|<z  :  3^  :  a  :  $c) ; 
{2131};  Fig.  113,  and  w  =  (±a  :  4*  :  a  :  *c);  {3145};"  Fig.  116. 

The  rhombohedron  e  occurs  more  frequently  than  the  unit  and 
is  shown  in  combination  with  the  rhombohedron  q  in  Fig.  1 1 1  and 
with  the  prism  m  in  Figs.  1 1 2  and  115. 

The  unit  rhombohedron  is  shown  in  combination  with  the  sca- 
lenohedron  v  in  Fig.  113,  and  with  the  two  scalenohedrons  v  and 
w  in  Fig.  1 1 6. 


FIG.  109. 


HEXAGONAL    SYSTEM.  51 

FIG.  no.  FIG.  in. 


FIG.  112. 


FIG.  113. 


FIG.  114. 


Hematite.  — Axes  a  :  c  =  i  :  1.365. 

Fig.  119  shows  the  unit  rhombohedron  /  with  the  basal  pina- 
coid  c  and  the  second  order  pyramid  n  =  (20,  :  20,  :  a  :  ^c) ;  { 2243 } ; 
FIG.  115.  FIG.  116. 


Fig.  117  shows  the  same  except  that  the  basal  pinacoid  is  replaced 
by  the  rhombohedron  g=  (a  :caa  :  a  :  \ c);  {1014};  and  Fig.  1 18 
shows  the  two  rhombohedrons  p  and  g. 

FIG.  117.  FIG.  118.  FIG.  119. 


Corundum.  — Axes  a\  c  =  I  :  1.363. 

The  unit  forms  of  hematite  and  corundum  are  practically  identical, 


52  CR  YSTALL  OGRAPHY. 

but  the  combinations  and  habit  are  very  different.  Fig.  1 20  shows 
a  second  order  pyramid  n  =  (20,  :  20, :  a  :  Jr);  {2243}.  Fig.  121 
shows  this  and  two  other  second  order  forms  o  =  (20,  \2a\  a:\c\\ 

V  o     /  ' 

{4483 } ;  and  a  =  (2a  :  2a  :  a  :  coc) ;  { 1 1 20}  ;  and  a  rhombohedron 
f  =  (a  :  co a  :  a  :  2c) ;  {2021}.  Fig.  122  shows  a  second  order 
pyramid  w  =  (20,  :  2a  :  a  :  2c) ;  {1121};  with  the  unit  rhombohe- 
dron /  and  the  basal  pinacoid  c. 


FIG.  120. 


FIG.  121. 


FIG.  122. 


RHOMBOHEDRAL  DIVISION,  HEMIMORPHIC  CLASS.*    20. 

No.  14.     Second  Hemimorphic  Tetartohedry,  Liebisch.     No.  20.      Rhombohedral 
Hemimorphic  Group,  Dana. 

The  common  mineral,  tourmaline,  and  the  ruby  silvers,  proustite 
and  pyrargyrite,  occur  in  forms  showing  different  groupings   of 

FIG.  123.  FIG.  124. 


faces  at  opposite  ends  of  the  vertical  axis.     That  is  the  forms  are 
symmetrical  to  a  three-fold  axis  and  to  three  planes  through  this  at 
60°  to  each  other,  Fig.  123. 
Choosing  Crystallographic  Axes. 

The  three-fold  axis  is  taken  as  the  vertical  (c)  axis  ;  the  others 
are  diagonal  to  the  planes  of  symmetry. 


*  The  forms  differ  so  markedly  from  those  of  the  preceding  and  following  class  that 
it  has  been  thought  wise  to  describe  them  in  detail. 


HEXAGONAL   SYSTEM.  53 

Tabulation  of  Seven  Type  Forms. 

NAME.  FACES.        WEISS.  MILLER, 

Each  face  oblique  to  c. 

1.  HEM.  DITRIGONAL  PYRAMID.  6  a  \na\pa  -.me  {hkll} 

2.  HEM.  HEX.  PYRAM.  SECOND  ORDER.     6  2a:2a:a:mc  {hh-2h-l} 

3.  HEM.  TRIGONAL  PYRAM.  FIRST  ORDER.  3  a  :  co  a  :  a  :  me  [kohl } 
Each  face  perpendicular  to  c. 

4.  BASAL  PLANE.  i  oo  a  :  coa  :  co  a  :c  {0001} 
Each  face  parallel  to  c. 

5.  DITRIGONAL  PRISM.  6  a :  na  \pa :  oo  c  {hkto} 

6.  HEXAG.  PRISM  SECOND  ORDER.  6  za  :za  :a  :  co  c  {1120} 

7.  TRIGONAL  PRISM  FIRST  ORDER.  3  a  :  oo  a  :  a  :  oo  c  {1010} 

Description  of  the  Type  Forms. 

1.  HEMIMORPH.  DITRIGONAL  PYRAMID. — a  \na\pa\  me;  {hkll}. 
Six  faces,  Fig.  124,  each  cutting  all  horizontal  axes  at  simply 

related  distances  and  all  cutting  the  vertical  axis. 

2.  HEMIMORPH.  HEXAG.  PYRAMID  2°  ORDER.  —  20,  :  2a  :  a  :  me; 


Six  faces,  Fig.  125,  each  cutting  one  horizontal  axis  at  a  certain 
distance,  the  others  at  twice  that  distance,  and  the  vertical  axis  at- 
a  distance  not  simply  proportionate. 


FIG.  125. 


FIG.  126. 


3.  HEMIMORPH.   TRIGONAL   PYRAMID    i°    ORDER. — a  r  ay  a  : 
a  :  mc\  {hoJil}. 

Three  faces,  Fig.  1 26,  each  parallel  to  one  horizontal  axis,  cutting 
the  other  two  at  equal  distances,  and  the  vertical  axis  at  some  dis- 
tance not  simply  proportionate. 

4.  THE  BASAL  PLANE.  —  co  a  :  oo  a  :  oo  a\c\   {oooi  }. 
One  face  parallel  to  the  basal  axes. 

5.  DITRIGONAL  PRISM.  —  a  \na\pa\  oo  c\   {hklo}. 

Six  faces,  Fig.  127,  each  parallel  to  the  vertical  axis  and  cutting 
all  horizontal  axes  at  unequal  distances  simple  multiples  of  each 
other. 

6.  HEX.  PRISM  OF  SECOND  ORDER.— 2a\  2a\a\vzc\  {h-h-2h-o}. 
Previously  described.     See  Fig.  107. 

7.  TRIGONAL  PRISM  OF  FIRST  ORDER. — a  :  oo  a  :  a  :  oo  c\  { lolo}. 


54 


CR  YSTALLOGRAPHY. 


Three  vertical  faces,  each  parallel  to  one  horizontal  axis  and  in- 
tersecting the  others  at  equal  distances  from  the  center,  Fig.  128. 

FIG.  127.  FIG.  128. 


Combinations  in  the  Hemimorphic  Class. 

Tourmaline. — Axes  a\c=\  :  0.447. 

Fig.  129  shows  the  first  order  trigonal  prism  m,  the  second 
order  hexagonal  prism  a ;  at  the  upper  end  the  trigonal  pyramids 
of  first  order  ^>  =  (a  :  oo  a  :  a  :  r);  { 101 1);  and/  =  (a  :  oo  a  :  a  :  2c)\ 
{ 202 1 } ;  but  at  the  lower  end  the  trigonal  pyramid  p  only.  Fig, 
130  shows  mt  p  and  a,  but  does  not  so  evidently  reveal  the  hemi- 
morphic  symmetry.  Fig.  1 3 1  again  shows  m  and  a  central,  with 
at  one  end  /  and  at  the  other/. 

FIG.  129.  FIG.  130.  FIG.  131. 


\ 


OTHER  CLASSES  OF  SYMMETRY  IN  THE  RHOMBOHEDRAL  DIVISION. 

In  each  there  is  an  axis  of  three-fold  symmetry. 

1 6.  CLASS  OF  HEMIMORPH.  TRIGONAL  PYRAMID  3°  ORDER. 
The  three -fold  axis.    No  planes  or  center  of  symmetry.    Example 

sodium  periodate,  NaIO4'3H2O. 

17.  CLASS  OF  RHOMBOHEDRON  3°  ORDER. 

The  three-fold  axis  and  center  of  symmetry.    Examples  —  Dolo- 
mite, ilmenite,  willemite,  phenacite,  dioptase. 


HEXAGONAL   SYSTEM.  55 

1 8.  CLASS  OF  TRIGONAL  TRAPEZOHEDRON. 

The  three-fold  axis  and  three  two -fold  axes  of  symmetry  at  90° 
thereto.      Examples  —  Quartz,  cinnabar. 

19.  CLASS  OF  TRIGONAL  PYRAMID  3°  ORDER. 

The  three-fold  axis  and  one  plane  of  symmetry  at  90°  thereto. 
No  examples  known. 

22.    CLASS  OF  DlTRIGONAL  PYRAMID. 

The  three-fold  axis,  three  planes  at  60°  and  one  at  90°  to  the 
three.     No  examples  known. 


HEXAGONAL  DIVISION.     CLASS   OF  DIHEXAGONAL  PYRAMID.     27. 

No.  6.   Holohedral,  Liebisch.     No.  13.  Normal  Group,  Dana. 

A  few  minerals,  notably  beryl,  crystallize  in  forms  symmetrical 
to  one  horizontal  plane  and  to  six  vertical  planes  at  thirty  degrees 
to  each  other  and  to  one  six-fold  and  six  two-fold  axes  which  are 
the  lines  of  intersection  of  these  planes,  Fig.  132. 

Choosing  Crystallographic  Axes. 

The  six-fold  axis  is  chosen  as  the  vertical  r,  the  two-fold  axes  as 
the  horizontal  axes  a,  one  of  which  is  conventionally  placed  from 
left  to  right. 

Tabulation  of  the  Seven  Type  Forms. 

NAME.  FACES.           WEISS.  MILLER. 
Each  face  oblique  to  c. 

1.  DIHEXAGONAL  PYRAMID.  24  a  :  na  \pa  :  me  {hkll} 

2.  HEXAG.  PYRAMID  2°  ORDER.  12  2a  \2a\a\mc  {h-h.2h-l} 

3.  HEXAG.  PYRAMID  i°  ORDER.  12  a  :  co  a  :a  :  me  {kohl} 
Each  face  perpendicular  to  c. 

4.  BASAL  PINACOID.  2  co  a  :  co  a  :  co  a  :c        {0001} 
Each  face  parallel  to  c. 

5.  DIHEXAGONAL  PRISM.  12  a  \na\pa  :  me  {hklo\ 

6.  HEXAG.  PRISM  2°  ORDER.  6  2a  :  2a  :  a  :  co  c  {1120} 

7.  HEXAG.  PRISM  i°  ORDER.  6  a  :  as  a  :  a  :  co  c  {ioTo} 

Description  of  the  Type  Forms. 

i.  DIHEXAGONAL  PYRAMID. — a  :  na  \pa  :  me ;  {hkll}. 

Twenty -four  faces,  Fig.  133,  each  of  which  cuts  the  three  hori- 
zontal axes  at  unequal  distances,  simple  multiples  of  each  other ; 
and  the  vertical  axis  at  some  distance  not  simply  related  to  the 
others.  In  the  ideal  form  the  faces  are  scalene  triangles. 


CR  YSTALLOGRAPHY. 


2.  HEXAGONAL  PYRAMID  OF  SECOND  ORDER.  —  See  Fig.  104. 

3.  HEXAGONAL  PYRAMID  OF  FIRST  ORDER. — a  :  oo  a  :  a  :  mc\ 
{hohl}. 

Twelve  faces,  Fig.  1 34,  each  parallel  to  one  horizontal  axis,  cutting 
the  others  at  equal  distances,  and  the  vertical  axis  at  some  distance 
not  simple  proportionate.  In  ideal  forms  the  faces  are  isosceles 
triangles. 

4.  BASAL  PINACOID,  —  The  faces  c  of  Figs.  135  to  137. 
.  5.  DIHEXAGONAL  PRISM.  —  See  Fig.  1 06. 


FIG.  132. 


FIG.  133. 


FIG.  134. 


6.  HEXAGONAL  PRISM  OF  SECOND  ORDER. — See  Fig.  107. 

7.  HEXAGONAL  PRISM  OF  FIRST  ORDER. — See  Fig.  108  or  the 
faces  m  of  Figs.  135  to  137. 

Combinations  in  the  Class  of  Dihexagonal  Pyramid. 
Beryl. — Axes  a  :  c  =  I  :  0.499. 


FIG.  135. 


FIG.  136. 


FIG.  137. 


Fig.  135  shows  the  prism  of  first  order  m  and  basal  pinacoid  c ; 
in  Fig.  136  the  second  order  pyramid*?  =  (2  a  :  2a  :  a  :  2c] ;{ 1 121}; 
occurs  and  in  Fig.  137  the  unit  pyramid  p  is  also  present 


HEXAGONAL   SYSTEM.  57 

OTHER  CLASSES  IN  THE  HEXAGONAL  DIVISION. 

Each  with  an  axis  of  six-fold  symmetry. 

23.  CLASS  OF  THIRD  ORDER  HEMIMORPHIC  PYRAMID. — The  six- 
fold axis  only.     Example — nephelite. 

24.  CLASS  OF  HEXAGONAL  TRAPEZOHEDRON.  —  The  six-fold  axis 
and  six  2-fold  axes  of  symmetry  at  90°  thereto.       Example  — 
Barium-antimonyl    dextro-tartrate   potassium    nitrate,    Ba(SbO)2- 
(C4H406)2.KN03. 

25.  CLASS  OF  THIRD  ORDER  HEXAGONAL  PYRAMID.  — The  six- 
fold axis  and  a  plane  of  symmetry  at  90°  thereto.     Examples  — • 
Apatite,  pyromorphite,  mimetite,  vanadinite. 

26.  CLASS  OF  HEMIMORPHIC  DIHEXAGONAL  PYRAMID.  —  The  six- 
fold axis  and  six  planes  of  symmetry  at  30°  to  each  other  inter- 
secting therein.     Example  —  lodyrite. 


CHAPTER  VII. 

ISOMETRIC  SYSTEM. 

THE  Isometric  *  system  includes  all  crystal  forms  which  can  be 
referred  to  three  interchangeable  axes  at  right  angles  to  each  other, 
that  is  axes  about  which  there  are  equal  numbers  of  faces  grouped 
with  corresponding  faces  at  the  same  angles. 

Five  classes  are  distinguished,  of  which  three  include  nearly  all 
known  isometric  minerals. 

HEXOCTAHEDRAL  CLASS.     32. 

No.  I.   Holohedral,  Liebisch.     No.  I.   Normal  Group,  Dana. 

Symmetry  of  the  Class. 

There  are  three  planes  of  symmetry,  Fig.  138,  parallel  to  cube 
iaces,  and    six  planes    through  diagonally   opposite   cube   edges. 
There  are  also,  Fig.   139,  three  four-fold,  four  three-fold  and  six 
two-fold  axes  of  symmetry. 
Choosing  Crystallographic  Axes. 

The  three  axes  of  four-fold  symmetry  are  chosen  as  the  crystal- 
lographic  axes.  Usually  one  is  assumed  to  be  vertical  and  one  to 
extend  from  left  to  right. 

Tabulation  of  the  Seven  Type  Forms. 

NAME.  FACES.  WEISS.  MILLER. 

Each  face  intersects  all  axes. 


1.  HEXOCTAHEDRON.  48 

2.  TRAPEZOHEDRON.  24 

3.  TRISOCTAHEDRON.  24 

4.  OCTAHEDRON.  8 
Each  face  parallel  to  one  axis. 

5.  DODECAHEDRON.  12 

6.  TETRAHEXAHEDRON.  24  a   na :  co  a 
Each  face  parallel  to  two  axes. 

7.  CUBE.  6  a    CD  a:  co  a 

Description  of  the  Type  Forms. 

i.   HEXOCTAHEDRON.  —  a  :  na  :  ma ;   {hkl}. 

*  Also  called  Tesseral,  Tessular,  Regular,  Cubic  and  Monometric. 

58 


{hkl} 
{hkk} 
[hhl] 
{ill} 

{no} 

[hko] 


ISOMETRIC  SYSTEM. 


59 


Forty-eight  faces  each  cutting  the  three  axes  in  three  different, 
but  simply  proportionate  distances.  In  the  ideal  forms  the  faces 
are  scalene  triangles.  Fig.  140  shows  a  :  %a  :  3*2 ;  {321}. 


FIG.  138. 


FIG.  139. 


mi/.^ 

SX\  K/& 

i-^f^f* 


The  small  black  squares  and  triangles  indicate  axes  of  four-fold  and  three-fold  sym- 
metry respectively. 

2.  TRAPEZOHEDRON.  —  a  :  ma  :  ma  ;  {hkk}. 
Twenty-four  faces,  each  cutting  two  axes  equally  and  the  third 
in  some  shorter  distance  bearing  a  simple  ratio  to  the  others.     In 


FIG.  140. 


FIG.  141. 


FIG.  142. 


FIG.  143. 


the  ideal  form  the  faces  are  trapeziums.     Fig.  141  shows  a  :  2a  :  2a ; 

{211}. 

3.  TRISOCTAHEDRON. — a  :  a  :  ma\  {hhl}. 

Twenty -four  faces,  each  cutting  two  axes  at  equal  distances,  the 
third   axes  at  some   longer   distance  a  simple 
multiple  of  the  others.      In  the  ideal  forms  the 
faces   are  isosceles   triangles.     Fig.  142  shows 
r  =  (a  :  a  :  20) ;  {221}. 

4.  THE  OCTAHEDRQN.  —  a  :  a  :  a\  {m}. 
Eight  faces,  Fig.  143,  each  cutting  the  three 

axes  at  equal  distances.      In  the  ideal  form  the 
faces  are  equilateral  triangles. 

5.  TETRAHEXAHEDRON.  — a  :  na  :  coa  ;  {hko}. 

Twenty -four  faces,  Fig.  144,  each  parallel  to  one  axis  and  cut- 


6o 


CR  YSTALL  O  GRAPHY. 


ting  the  other  two  unequally  in  distances  bearing  a  simple  ratio  to 
each  other.  In  the  ideal  forms  the  faces  are  equal  isosceles  tri- 
angles. Fig.  144  shows  a  :  20,  :coa;  {210}. 


FIG.  144. 


FIG.  145. 


FIG.  146. 


6.  THE  DODECAHEDRON. — a  :  a  :  CD  a:  (no). 

'  c        ) 

Twelve  faces,  Fig.  145,  each  parallel  to  one  axis  and  cutting  the 
others  at  equal  distances.     In  the  ideal  form  each  face  is  a  rhombus. 

7.  THE  CUBE. — a  :  oo  a  :  oo  a  ;   {100}. 


FIG.  147. 


FIG.  148. 


FIG.  149. 


f 

ox*' 

\)  r— 

a- 

4 

Six  faces,  Fig.   146,  each  parallel  to  two  axes.     In  the  ideal 
forms  the  faces  are  squares. 
Combinations  in  the  Hexoctahedral  Class. 

The  most  frequently  occurring  forms  are  the  cube  a,  the  octahe- 
FIG.  150.  FIG.  151.  FIG.  152. 


dron/,  the  dodecahedron  </,  and  the  trapezohedron  n  =  (a  :  2a  :  2a)\ 
{211}.     The  other  forms  usually  occur  modifying  these. 

The  cube  a  and  dodecahedron  d,  Figs.  147,  148,  are  combined 
in  crystals  of  fluorite,  argentite  and  cuprite.     The  cube  and  octa- 


ISOMETRIC  SYSTEM. 


61 


hedron  p,  Figs.  149,  1 50  and  151,  are  very  frequently  combined  in 
fluorite,  galenite,  silver,  sylvite  and  many  other  minerals.  The 
octahedron,/,  and  dodecahedron,  d,  Figs.  152  and  153,  are  fre- 
quently found  in  spinel,  magnetite,  franklinite  and  cuprite,  while 

FIG.  153.  FIG.  154.  FIG.  155. 


the  three  together,  cube,  dodecahedron  and  octahedron,  Fig.  154, 
occur  in  smaltite,  galenite  and  fluorite.  The  tetrahexahedron  e  =3 
(a  :  2a  :  oo  a);  {210}  ;  is  found  with  the  cube  in  fluorite,  Fig.  155. 

FIG.  156.  FIG.  157.  FIG.  158.' 


The  trapezohedron  n  =  (a\  2a\  20) ;  {211}  ;  is  common  in  analcite, 
garnet  and  amalgam,  either  combined  with  the  dodecahedron,  Figs. 
156  and  158  or  with  the  cube,  Fig.  157. 

FIG.  159.  FIG.  160.  FIG.  161. 


Another  trapezohedron  o  =  (a 


The  tris octahedron  r  =  (a  :  a 


:  30) ;  {311};  occurs  in  spinel 


and  magnetite  either  with  the  octahedron,  Fig.  159,  or  with  both 
octahedron  and  dodecahedron,  Figs.  160  and  161. 


20)  ;  {221 };  occasionally  occurs, 


especially  in  galenite  and   magnetite,  combined  with   octahedron 


62 


CR  YSTALLOGRAPPIY. 


and  dodecahedron,  Fig.  162.  The  hexoctahedron  /  =  (a  :  2a  :  4^) ; 
{421}  ;  occurs  modifying  cubes  of  fluorite,  Fig.  163,  and  another 
hexoctahedron  s  =  (a  :  \a  :  $a)  ;  {321 }  ;  occurs  in  garnet,  Fig.  164. 


FIG.  162. 


FIG.  163. 


FIG.  164. 


HEXTETRAHEDRAL   CLASS.     31. 

No.  2.  Tetrahedral  Hemihedry,  Liebisch.     No.  3.   Tetrahedral  Group,  Dana. 

FIG.  165.  In  this  class  of  isometric  forms,  to  which 

crystals  of  the  diamond,  tetrahedrite,  spha- 
lerite and  boracite  belong,  the  shaded  planes 
of  Fig.    138  are  no   longer  planes  of  sym- 
metry,  and  the   symmetry  is  restricted  to 
the  diagonal  planes  shown  in  Fig.  165  and 
to  the   four  three-fold  and  three  two-fold 
axes  formed  by  their  intersection. 
Choosing  Crystallographic  Axes. 
The  three  axes  of  two-fold  symmetry  are  chosen  as  the  crystallo> 
graphic  axes. 

Tabulation  of  the  Seven  Type  Forms. 

FACES.  WEISS. 


NAME. 
Each  face  intersects  all  axes. 

1.  HEXTETRAHEDRON.  24 

2.  TRISTETRAHEDRON.  12 

3.  DELTOHEDRON.  12 

4.  TETRAHEDRON.  4 
Each  face  parallel  to  one  axis. 

5.  TETRAHEXAHEDRON.          24 

6.  DODECAHEDRON.  12 
Each  face  parallel  to  two  axes. 

7.  CUBE.  6 


na  :  ma 
ma  :  ma 
a  :  ma 
a  :  a 

net :  oo  a 
a  :  co  a 

co  a  '.  co  a 


MILLER. 

{hkl} 
{hkk} 
[hhl] 
{III} 


{no} 

{100} 


Descriptions  of  the  Type  Forms. 

i .   HEXTETRAHEDRON.  —  a\na\  ma ;   {hkl}. 

Twenty-four  faces  each  cutting  the  three  axes  in  three  different, 


rSOMETRIC  SYSTEM. 


but  simply  proportionate,  distances.     In  the  ideal  forms  the  faces 
are  scalene  triangles.      Fig.  166. 

2.  TRISTETRAHEDRON.  —  a  :  ma  :  ma  ;   [hkk] . 

Twelve  faces,  Fig.  167,  each  cutting  two  axes  equally  and  the 


FIG.   166. 


FIG.   167. 


third  in  some  shorter  distance  bearing  a  simple  ratio  to  the  others. 
In  the  ideal  form  the  faces  are  isosceles  triangles. 

3.   DELTOHEDRON. — a:a:ma\   {hhl}. 

Twelve  faces,  each  cutting  two  axes  equally  and  the  third  in 
some  longer  distance  a  simple  multiple  of  the  others.  In  the  ideal 
form  the  faces  are  trapeziums.  Fig.  1 68  shows  r  =  (a  :  a  :  20) ; 


221}. 


FIG.   168. 


FIG.  169. 


4.  THE  TETRAHEDRON.  —  a  :  a  :  a;   {m}. 

Four  faces,  Fig.  169,  each  cutting  the  three  axes  at  equal  dis- 
tances. In  the  ideal  form  the  faces  are  equilateral  triangles. 

5.  TETRAHEXAHEDRON.  —  Fig.  144. 

6.  THE  DODECAHEDRON. — Fig.  145. 

7.  THE  CUBE.  —  Fig.  146. 
Combinations  in  the  Hextetrahedral  Class. 

The  characteristics  of  the  crystals  of  this  group  are  best  shown 
in  combinations  of  forms,  since  the  simple  forms  are  comparatively 
rare  and  the  predominating  form  is  frequently  the  cube. 

The  combination  of  the  positive  and  negative  tetrahedrons,  Fig. 
170  occurs  in  crystals  of  sphalerite  and  tetrahedrite.  The  combi- 


64 


CR  YSTALLOGRAPHY. 


nation  of  the  tetrahedron  and  cube  a,  Figs.  171  and  172,  is  com- 
mon in  boracite  and  pharmacosiderite.  The  tetrahedron  with  the 
dodecahedron  d,  Fig.  173,  occurs  in  tetrahedrite,  and  with  both 
cube  and  dodecahedron,  Fig.  174,  in  boracite. 


FIG.  170. 


FIG.  171. 


FIG.  172. 


Figs.  175  and  176  are  crystals  of  tetrahedrite.  In  Fig.  175  the 
negative  form  of  n  —  (a  :  2a  :  20) ;  {211};  occurs  and  in  Fig.  176 
the  positive  form  of  n  with  the  dodecahedron  d. 


FIG.   173. 


FIG.   174. 


FIG.  175. 


Fig.  177  includes  the  dodecahedron  d,  the  deltohedron  r  —  (a  : 
a  :  20) ;  {221};  and  the  tristetrahedrons  o  =  (a  :  ^a  :  30) ;  {311}; 
and  n  =  (a  :  2a  :  20) ;  {211}  ;  Fig.  178  shows  the  hextetrahedron  s 


FIG.  176. 


FIG.  177. 


FIG.  178. 


=  (a  :  | a  :  3^) ;  {321};  combined   with  the   cube  and   tetrahexa- 
hedron  g  .-=  (a  :  \a  :  oo  a) ;  (3  20} . 


ISOMETRIC  SYSTEM. 


CLASS   OF   THE  DIPLOID.     30. 

No.  4.   Pentagonal  Hemihedry,  Liebisch.     No.  2.   Pyritohedral  Group,  Dana. 

Symmetry  of  the  Class. 

Crystals  of  the  common  mineral  pyrite  FIG.  179. 

and  of  the  minerals  cobaltite  and  smaltite 
are  symmetrical  to  three  planes  at  right 
angles  and  to  three  axes  of  two-fold  and 
four  axes  of  three-fold  symmetry,  as 
shown  in  Fig.  179. 
Choosing  Crystallographic  Axes. 

The  three  axes  of  two-fold,  symmetry 
are  chosen  as  the  crystallographic  axes. 
Tabulation  of  the  Seven  Type  Forms. 

FACES.  WEISS. 


NAME. 
Each  face  intersects  all  the  axes. 

1.  DIPLOID.  24 

2.  TRAPEZOHEDRON.  24 

3.  TRISOCTAHEDRON.  24 

4.  OCTAHEDRON.  8 
Each  face  parallel  to  one  axis. 

5.  PYRITOHEDRON.  12 

6.  DODECAHEDRON.  12 
Each  face  parallel  to  two  axes. 

7.  CUBE.  6 


na  :  ma 
nia  :  nia 
a  :  ma 

a  :  a 


co  a  :  oo  a 


MILLER. 

{hkl} 
{hkk} 
{hhl} 
{in} 


{110} 
{100} 


Description  of  the  Type  Forms. 

i.   DIPLOID. — a  :  na  :  ma  ;    {hkl}. 

Twenty-four  faces  each  cutting  the  three  axes  in  three  different, 
but  simply  proportionate,  distances.  In  the  ideal  form  the  faces 
are  trapeziums.  Fig.  180  shows  a  positive  form. 

FIG.  1 80.  FIG.  181. 


2.  TRAPEZOHEDRON,  Fig.  141. 

3.  TRISOCTAHEDRON,  Fig.  142. 

4.  THE  OCTAHEDRON,  Fig.  143. 
6 


66 


CR  YSTALLOGRAPHY. 


5.  PYRITOHEDRON.  —  a  :  na  :  coa;   {.hko}. 

Twelve  faces,  Fig.  1 8 1 ,  each  parallel  to  one  axis  and  cutting  the 
other  two  unequally  in  distances  bearing  a  simple  ratio  to  each 
other.  In  the  ideal  forms  the  faces  are  pentagons. 

6.  THE  DODECAHEDRON,  Fig.  145. 

7.  THE  CUBE,  Fig.  146. 
Combinations  in  the  Class  of  the  Diploid. 

FIG.  182.       '  FIG.  183.  FIG.  184. 


Fig.  182  shows  the  pyritohedron  e  =  (a  :  2a  :  coo) ;  {210};  with 
the  cube  a.  Figs.  183  and  184  show  the  same  form  with  the 
octahedron  /. 

FIG.  185.  FIG.  186,  FIG.  187. 


Fig.  185  shows  the  three  forms  combined.  Fig.  186  shows  the 
same  pyritohedron  e  and  octahedron  /  combined  with  the  diploid 
s  =  (a  :  \a  :  $a) ;  {321};  and  Fig.  187  shows  this  diploid  with  the 
cube  and  octahedron. 


OTHER  CLASSES  IN  THE  ISOMETRIC  SYSTEM. 

28.  CLASS  OF  THE  TETARTOID. —Three  axes  of  two-fold  sym- 
metry at  90°  to  cube  faces  and  four  of  three-fold  through  opposite 
corners  of  the  cube.      Example  —  Ullmannite. 

29.  CLASS  OF  THE  GYROID.  —  Three  axes  of  four-fold  symmetry, 
at  90°  to  cube  faces,  four  of  three-fold  through  opposite  corners  of 


cube,  six  of  two-fold   through  diagonally  opposite  edges, 
amples  —  Sylvite,  sal-ammoniac. 


Ex- 


ISOMETRIC  SYSTEM.  6? 

IMPORTANT   SUPPLEMENT  ANGLES   BETWEEN  ADJACENT  FACES    IN 
ISOMETRIC  CRYSTALS. 

CUBE  90°  OCTAHEDRON  70°  31'  DODECAHEDRON  60° 

CUBE  TO  OCTAHEDRON  54°  44'  CUBE  TO  DODECAHEDRON  45° 

OCTAHEDRON  TO  DODECAHEDRON  35°  i^ 

Polar  Edge.  Other  Edges. 

Tetrahexahedra  320  46°  n'  22°  37' 

210  36  52  36  52 

3io  25  50  53  17 

Pyritohedra  320  67    22  62    30 

210  53      7  66    25 
310  36    52  72    32 

Edge  in  Axial  Plane. 

Trapezohedra                       311                          35°    5'  50  28 

211  48    ii  33  33 
322                          58      2  19  45 

Edge  in  Diagonal.       Edge  in  Axial  Plane.        Other  Edges. 

Hexoctahedra     321        21°  47'        31°  o'        21°  47 
421        17  45        25  12        35  57 


CHAPTER  VIII. 

THE   GROUPING   OF   CRYSTALS  AND   THEIR 
IMPERFECTIONS. 

Crystals  are  more  frequently  grouped  than  isolated  and  with 
respect  to  their  grouping  may  be  divided  into  symmetrically 
grouped  or  "twin"  crystals  and  unsymmetrically  grouped  crystals, 
usually  known  as  crystal  aggregates. 

TWIN    CRYSTALS. 

Crystals  frequently  form  which  consist  of  two  individuals,  one 
of  which  is  reversed  with  respect  to  the  other.  In  such  crystals 
re-entrant  angles  are  common. 

FIG.  188.  FIG.  189. 


Such  growths  are  called  twin  crystals.  If  the  individuals  inter- 
penetrate they  constitute  a  penetration  twin.  If  simply  in  contact 
along  a  certain  plane  they  constitute  a  contact  twin.  Fig.  188 
shows  a  contact  twin  octahedron  very  frequent  in  the  spinel 
group.  Fig.  189  shows  the  corresponding  penetration  twin. 

Symmetry  of  Twin  Crystals. 

The  crystal  may  be  (a)  symmetrical  only  to  a  line  called  a 
"twin  axis,"  always  parallel  to  a  possible  edge  of  the  crystal  but 
never  an  axis  of  two-,  four-  or  six-fold  symmetry.  Fig.  190  shows 
pyroxene  with  the  twin  axis  parallel  to  a  prism  edge.  Fig.  191 
shows  the  "Iron  Cross"  of  pyrite,  a  twin  pyritehedron  with  the 
twin  axis  a  cubic  edge.  Fig.  192  shows  quartz  with  the  twin  axis 
parallel  a  prism  edge;  these  frequently  penetrate  and  as  the  positive 

68 


THE    GROUPING    OF   CRYSTALS. 


69 


rhombohedron  of  one  coincides  with  the  negative  of  the  other, 
the  twin  structure  is  then  only  recognized  by  etching. 


FIG.  190. 


FIG.  191. 


FIG.  192. 


(b)  Symmetrical  to  a  twin  axis  and  also  to  a  "twin  plane"  at 
right  angles  to  the  axis.  The  plane  is  always  parallel  to  a  possible 
face  of  the  crystal  but  never  a  plane  of  symmetry  for  either 
individual. 

Fig.  193  shows  an  aragonite  twin,  the  twin  plane  a  prism  face. 
Fig.  194  shows  a  twin  cube,  the  twin  plane  being  an  octahedral 


FIG.  193. 


FIG.  194. 


FIG.  195. 


face.     Fig.  195  shows  a  twin  of  albite,  the  brachy  pinacoid  being 
the  twin  plane. 

Repeated  Twinning. 

Frequently  there  is  a  repetition  of  the  twinning,  a  third  indi- 
vidual occurring  reversed  upon  the  second,  a  fourth  upon  the 
third,  and  so  on. 

If  the  successive  twin  planes  are  parallel  the  phenomenon  is 
called  "poly synthetic  twinning"  the  individuals  may  be  thin 
lamellae  and  the  re-entrant  angles  striae.  Fig.  196  shows  the 
polysynthetic  twinning  of  albite. 


CR  YSTALLOGRAPHY. 


If  the  successive  twin  planes  are  oblique  to  each  other  repetition 
may  lead  to  " circular  forms"  as  in  orthorhombic  marcasite  with 
the  prism  face  the  twin  plane,  Fig.  197,  because  the  prism  angle 
74°  55'  is  approximately  one  fifth  of  360°. 


FIG.  196. 


FIG.  197. 


FIG.  198. 


Sometimes  the  "circular  form"  is  pseudosymmetrical  and  ap- 
proximates a  higher  class  of  symmetry;  for  instance,  repetition  of 
Fig.  193  leads  to  pseudohexagonal  forms,  Fig.  198,  the  prism  angle 
being  63°  48'. 

CRYSTAL   AGGREGATES. 

Crystals  of  any  substance  even  when  not  grouped  symmetrically 
may  be  grouped  with  a  degree  of  regularity  characteristic  of  that 
particular  occurrence  of  the  substance  and  sometimes  character- 
istic of  many  occurrences. 

The  Individual  Crystals  of  an  Aggregate. 

Unless  formed  while  floating,  like  snow  crystals  in  air,  or  gypsum 
crystals  in  clay,  or  leucite  in  a  molten  magma,  the  individual 
crystal  will  not  be  completely  bounded  by  plane  faces.  If  formed 
in  a  cavity  attached  to  and  projecting  from  the  rock  the  opposite 
ends  will  be  plane  faced  and  so  much  of  the  rest  as  is  free.  As 
compactness  increases  the  plane  faces  diminish  in  number  and 
may  entirely  disappear,  although  the  individual  may  still  be 
evident.  Finally,  the  individuals  may  be  microscopic  and  the 
mass  dense. 

Terms  Dependent  on  the  Shape  and  Grouping  of  the  Individual 
Crystals  of  an  Aggregate. 

Whether  showing  plane  faces  or  not  the  individuals  may  be 
distinguished  as  to  their  shape  by  such  terms  as : 


THE    GROUPING    OF   CRYSTALS.  71 

Columnar — when  the  individual  crystals  are  relatively  long  in 
one  direction,  Fig.  199. 

Bladed — a  variety  of  columnar  in  which  the  columns  are 
flattened  like  a  knife  blade. 

Fibrous — a  variety  of  columnar  in  which  the  columns  are  slender 
threads  or  filaments,  Fig.  200. 

Lamellar — when  the  individual  crystals  appear  as  layers  or 
plates,  either  straight  or  curved. 

Foliated — a  variety  of  lamellar  in  which  the  plates  separate  easily. 


FIG.  199. 


FIG.  200. 


Columnar  Beryl. 


Fibrous  Serpentine. 


Micaceous — a  variety  of  lamellar  in  which  the  leaves  can  be 
obtained  extremely  thin. 

Granular — when  the  individual  crystals  are  angular  grains, 
either  coarse  or  fine. 

Impalpable  or  dense — a  variety  of  granular  in  which  the  grains 
are  invisible  to  the  naked  eye. 

With  respect  to  the  grouping,  the  individual  crystals  may  be: 

Parallel — in  crystals  with  plane  faces  this  may  extend  to  all  cor- 
responding faces  and  edges,  Fig.  201,  and  may  be  recognized  by  the 
simultaneous  reflection  of  light  from  parallel  faces,  or  it  may  be 
partial  with  respect  to  an  edge  or  a  face. 


72 


CR  YSTALLOGRAPHY. 


In   crystals   lacking   plane   faces   there  result   parallel   fibers, 
blades,  columns,  lamellae,  etc. 


FIG.  201. 


Parallel  Copper  Crystals. 

Radiating — diverging  from  a  common  center. 
Reticulated — crossing  like  the  meshes  of  a  net,  Fig.  202. 
Resetted — overlapping  like  the  petals  of  a  rose. 
Drusy — minute  crystals  resting  close  together  on  a  common 
underlayer,  giving  a  rough  sand-paper  like  surface. 

FIG.  202. 


Reticulated  Stibnitc. 


THE   GROUPING    OF   CRYSTALS 
FIG.  203. 


73 


Reniform  Hematite. 
FIG.  204. 


Botryoidal  Prehnite. 
FIG.  205. 


Stalactitic  Gibbsite. 


74 


CR  YSTALLOGRAPHY. 


Terms  Describing  the  External  Shape  of  Aggregates. 

Many  terms  are  used.     The  more  important  of  these  are: 
Reniform — with  the  shape  of  a  kidney,  Fig.  203. 
Botryoidal — resembling  a  bunch  of  grapes,  Fig.  204. 
Mammillary — natter  but  rounded  shapes. 
Pisolitic — small  rounded  particles  the  size  of  a  pea. 
Oolitic — similar  but  smaller  like  fish  roe. 
Nodular — occurring  in  separate  rounded  lumps  or  nodules. 
Stalactitic — in* hanging  cones  like  icicles,  Fig.  205,  206. 

FIG.  206. 


Stalactite  of  Limonite. 

Cockscomb — the  free  ends  of  radiating  crystals  forming  a  ridge. 

Plumose — like  a  feather. 

Sheaf -like — resembling  a  sheaf  of  wheat. 

Arborescent  or  Dendritic — branching  like  a  tree,  Fig.  207. 

Mossy — similar  to  dendritic  but  a  more  minute  structure. 

Coralloidal — like  coral  in  form. 

Amygdaloidal — almond-shaped. 

Wire-like — as  in  silver. 

Geode — a  hollow  nodule  lined  with  crystals. 

TERMS    OF    GROWTH   AND    "HABIT." 

Dependent  upon  the  conditions  of  growth  crystals  may  be 
" Embedded"  in  a  groundmass,  Fig.  208,  or  "Attached"  by  one  end 
to  the  rock  and  extending  into  free  space.  The  former  has  a  chance 
for  complete  plane  faced  boundaries,  the  latter  necessarily  lacks 
some  of  the  faces. 


THE    GROUPING    OF   CRYSTALS. 
FIG.  207. 


75 


Arborescent  Copper. 

Habit. 

The  term  habit  is  used  to  express  the  usual  or  prevailing  shape 
of  the  crystals  of  a  substance.  The  habit  under  one  set  of  condi- 
tions at  formation  is  fairly  constant,  both  as  to  occurring  forms 
and  their  relative  development.  The  habit  for  another  set  of 

FIG.  208. 


76 


CR  YSTALL  OGRAPHY. 


conditions  (another  locality)  may  involve  just  the  same  forms 
with  a  different  relative  development  or  the  forms  themselves 
may  be  different. 

The  principal  terms  of  habit  are: 

Prismatic  Habit. 

Notably  elongated  in  one  direction,  which  is  liable  to  be  the 
direction  of  the  optic  axis  or  of  an  axis  of  symmetry  or  of  the 
intersection  of  cleavages. 

Tabular  Habit. 

Notably  extended  parallel  some  prominent  plane,  either  a 
cleavage  or,  if  uniaxial,  at  right  angles  to  the  optic  axis. 

Other  terms,  as  cubic,  octahedral,  pyramidal,  with  the  prefix 
habit,  imply  that  the  usually  dominant  form  is  the  cube,  octahedron 
and  pyramid  respectively. 

Figs.  209  and  210  represent  quartz  crystals  composed  of  the 
same  common  forms  m  { lolo  j ,  p  { ioli } ,  p  {oiTi } ,  in  Fig.  209  the 


FIG.  209. 


FIG.  210. 


FIG.  211. 


equivalent  faces  are  equal  sized,  in  Fig.  210  they  are  not,  but  in 
each  case  equivalent  faces  are  directions  of  equivalent  structure, 
and  the  crystal  symmetry  and  interfacial  angles  are  the  same  in 
both.  Sometimes  the  forms  appear  to  be  of  higher  or  lower 
symmetry  than  that  proper  to  the  substance,  for  instance,  the  not 
unusual  combination  in  zircon  of  the  forms  p  {in}  and  a  =  {100} 
may  develop  as  in  Fig.  211  suggesting  the  isometric  dodecahedron, 
although  the  supplement  angles  p  :  p  and  p  :  a  instead  of  being  60° 
are  respectively  56°  40'  and  61°  40'.  Conversely,  the  isometric 
dodecahedron  sometimes  develops  so  as  to  closely  imitate  the  prism 
fiooj  and  pyramid  {in}  of  zircon. 


THE    GROUPING    OF   CRYSTALS.  77 

Skeleton  Crystals. 

If  the  material  comes  faster  to  the  edges  than  elsewhere  the 
faces  become  relatively  depressed  or  hopper-shaped  as  in  cuprite, 
Fig.  212,  or  if  the  dominant  accretion  is  at  the  solid  angles  com- 
posite patterns  like  those  of  snow  crystals  or  gold  may  result. 

FIG.  212.  FIG.  213.  FIG.  214. 


Sometimes  the  faces  build  up  most  quickly,  leaving  the  edges 
relatively  depressed,  as  in  quartz. 

(d)  Microlites* — Microscopic,  not  easily  identified  rods  and 
needles  frequently  rounded  or  frayed  at  the  ends,  Fig.  213. 

IRREGULARITIES    OF  FACES    OF   CRYSTALS. 

The  perfectly  smooth  and  plane  crystal  is  difficult  to  find, 
except  in  very  minute  crystals. 
Striated  Faces. 

Crystal  faces  are  frequently  marked  by  parallel  lines  or  fine 
"grooves"  called  "striations"  each  of  which  is  bounded  by  two 
definite  planes.  That  is,  they  are  parallel  to  edges.  Usually  they 
line  a  face  in  one  direction  only,  sometimes  in  two,  or  more  often 
three,  and  frequently  not  intersecting  but  branching  feather-like 
from  a  common  line. 

They  may  occur  on  simple  crystals  as  in  chabazite,  but  often  are 
due  to  repeated  or  polysynthetic  twinning,  Fig.  196.  If  the  indi- 
viduals are  thin  the  reentrant  angles  become  grooves  or  striations. 
Fig.  215  shows  twinning  striations  on  a  magnetite  crystal  from 
Port  Henry,  N.  Y.* 

At  other  times  striations  result  from  an  oscillation  or  contest 
between  two  crystal  forms.  This  is  true  of  the  striations  on  the 

*  Crystallites,  a  name  applied  to  minute  forms  not  crystalline  in  shape,  are  now 
held  to  be  molecular  mixtures  of  different  substances. 


CR  YSTALLOGRAPHY. 


prism  faces  of  quartz,  which  are  due  to  an  alternate  formation 
of  prism  and  rhombohedron ;  or  the  striations  on  pyrite  due  to 
an  oscillation  between  the  cube  and  the  pyritohedron,  Fig.  215. 

FIG.  215. 


Striated  Pyrite,  Aspen,  Colo.     After  S.  Smillie. 

False  or  Apparent  Faces. 

Oscillatory  stria  may  be  so  frequent  as  to  give  rise  to  an  apparent 
plane  made  up  of  these  edges.     It  will  not  reflect  a  signal.     Ap- 
parent faces  may  also  result  from  the  contact  of  the  crystal  during 
growth  with  an  already  formed  crystal. 
Vicinal  Faces. 

Prominent  faces  with  simple  indices  are  sometimes  replaced 
wholly  or  in  part  by  flattened  pyramids,  the  faces  of  which  are 
in  definite  zones  but  with  complicated  indices.  Concentration 
currents  which  are  too  feeble  to  completely  cover  the  larger  faces 
are  a  possible  explanation.  Like  etch  figures,  they  usually  belong 
to  forms  which  prove  the  true  symmetry  of  the  crystal. 
Roughened  or  Coated  Faces. 

The  faces  of  crystals  may  be  coated  with  minute  crystals  of  the 
same  or  some  other  substance.     Sometimes  only  particular  faces 
are  so  covered.     Secondary   growths   and  natural   etchings  may 
also  roughen  faces. 
Curved  Faces. 

Curved  faces  are  not  frequent  and  are  nearly  always  convex. 
They  may  be  due  to  strains  after  formation  which  exceeded  the 
elastic  limit  as  in  stibnite,  gypsum,  galenite. 


THE    GROUPING    OF   CRYSTALS.  79 

Sometimes  the  edges  appear  to  have  been  melted  as  in  many 
apatites,  augites  and  hornblendes. 

Apparently  Curved  Faces. — A  rounded  effect  may  be  produced 
by  many  true  faces  in  one  zone,  as  in  beryl,  or  by  a  series  of  vicinal 
faces  each  nearly  parallel  to  the  preceding  as  in  diamond. 

Crystals  also  appear  curved  because  composed  of  individual 
smaller  crystals  only  approximately  parallel  as  in  dolomite  or 
siderite. 

INTERNAL   PECULIARITIES. 

Zonal  Structures. 

The  deposition  of  layer  after  layer  on  the  growing  crystal  is 
not  usually  observable  unless  there  has  been  an  intermittent 
growth  or  some  change  in  the  composition  of  the  material  de- 
posited. Intermittent  growth  permits  between  layers  the  de- 
positing of  dust  or  fine  lamellae  of  a  foreign  substance  and  this 
may  be  repeated  several  times.  Such  may  be  the  explanation  of 
"phantoms"  in  which  an  earlier  stage  of  growth  is  delicately 
outlined  as  in  quartz,  gypsum  and  fluorite. 

There  may  also  result  parallel  planes  of  easy  separation,  e.  g.t 
capped  quartz. 

Often  the  inner  kernel  is  like  the  outer  hull  in  shape  but  it 
may  be  a  different  form,  e.  g.,  calcite  kernel  (0112)  hull  (ion). 

Change  of  composition  tends  to  layers  of  different  colors  or 
transparency,  any  of  which  reveal  the  zonal  structure.  California 
tourmalines  are  good  examples. 

The  partial  decomposition  of  a  crystal  may  also  develop  or 
make  visible  the  zonal  structure. 

Hour- Glass  Structure. 

This  is  essentially  a  variety  of  zonal  structure  with  the  revealing 
of  the  "growth  pyramids"  upon  each  face  of  the  nucleus,  the  total 
shape  suggesting  an  hour  glass  as  in  many  augites. 

Inclusions. 

Foreign  substances  shut  in  a  crystal  during  rapid  solidification 
may  be  solid,  liquid  or  gaseous.  Solid  inclusions  may  be  separa- 
tions from  enclosed  magma  or  aqueous  solution,  or  due  to  altera- 
tion or  be  mechanically  retained  during  crystallization  of  an 
impure  mixture.  Such  solids  are: 


8o 


CR  YSTALLOGRAPHY. 


(a)  Glass,  from  enclosed  magma. 

(b)  Crystals  from  magma  or  solutions,  often  microlites  or  long 
prismatic  like  rutile  (Fig.  216),  actinolite  or  tourmaline  in  quartz, 
or  plate-like,  as  in  the  minute  scales  of  iron  oxide  in  hypersthene, 

sunstone  or  carnallite. 

FIG.  216. 


Rutile  in  Quartz,  N.  C- 

(c)  Sand  or  other  associated  material  as  in  the  crystals  of  calcite 
called  Fontainebleau  limestone,  which  contains  sometimes  as 
much  as  sixty  percent  of  silica. 

These  solids  may  show  no  evidence  of  arrangement  or  may  be 
definitely  arranged  as  in  the  case  of  the  magnetite  in  mica  or  the 
carbonaceous  material  in  chiastolite  as  shown  in  successive  sections 

of  a  crystal  in  Fig.  217. 

FIG.  217. 


Liquid  Inclusions. 

Chalcedony,  quartz,  topaz,  halite,  and  other  species  frequently 
contain   microscopic   cavities   partially   filled   with   water,   brine, 
liquid  carbonic  acid  and  other  liquids. 
Gaseous  Inclusions. 

Occur  in  round  and  simple  cavities  or  negative  crystals.* 
Usually  the  gas  is  under  high  pressure  and  may  be  water  vapor, 
hydrocarbons  such  as  marsh  gas,  nitrogen  and  carbonic  oxide. 


THE   GROUPING    OF   CRYSTAL.  8 1 

INTERGROWTHS  AND   PARALLEL  GROWTHS   OF  TWO    DIFFERENT 

MINERALS. 

Crystals  of  two  minerals  forming  at  the  same  time  may : 

(a)  Mutually  penetrate  each  other,  for  example,  quartz  and 
orthoclase  in  graphic  granite. 

(b)  Arrange  themselves  with   a  certain  face  or  edge  of  one 
parallel  to  a  corresponding  part  of  another;  for  example,  staurolite 
and  cyanite  with  brachy  pinacoids  parallel. 

(c)  The    larger    mass    may    orient    the    smaller;  for   example, 
prisms  of  rutile  on  hematite  with  the  prism  edge  of  rutile  perpen- 
dicular to  an  edge  of  hematite  and  the  prism  face  of  rutile  in 
contact  with  basal  plane  of  hematite. 

Form  of  Amorphous  Minerals  (Colloids  and  Glasses). 

Natural  minerals  of  colloidal  origin  (see  p.  235)  are  frequently 
reniform  (kidney-shaped),  botryoidal  (grape-shaped),  stalactitic, 
and  in  other  rounded  shapes.  With  lack  of  space  they  may  be 
dendritic.  Often  cracked  as  result  of  drying. 

Natural  glasses  often  show  fluidal  texture. 

*  Supposed  to  form  when  the  shut  in  liquid  contains  more  molecules  of  the  same 
material  as  the  host.  Their  separation  against  the  walls  of  cavities  give  the  faces 


CHAPTER   IX. 

THE   DETERMINATION   OF  THE  GEOMETRICAL 
CONSTANTS   OF   A   CRYSTAL. 

This  chapter  outlines*  a  simple  method  in  crystal  examination 
with  a  one  circle  goniometer,  stereographic  projection  and  graph- 
ical or  zonal  solutions,  under  the  principal  divisions  of: 

I.  Measurement  of  the  Interfacial  Angles. 
II.  Stereographic  Projection. 

III.  Determination   of   Symmetry   and   Selection   of   Elemental 

Faces. 

IV.  Zonal  and  Graphic  Determination  of  Indices. 
V.  Calculation  of  Axial  Elements. 

To  this  is  added: 
VI.  Crystal  Drawing. 

I.     MEASUREMENT   OF  INTERFACIAL   ANGLES. 

The  angles  between  smooth  bright  faces  can  be  measured  to 
half  minutes  or  even  closer  on  a  one  circle  reflecting  goniometer 
as  follows: 

The  available  crystals  are  carefully  examined.  Good  crystals 
with  bright  smooth  faces  are  more  apt  to  be  found  among  little 
crystals  than  large  ones.  During  examination  they  are  handled 
by  either  a  pencil  of  wax  or  by  the  forceps,  never  by  the 
fingers. 

Each  selected  crystal  is  studied  with  a  hand-glass  and  a  sketch 
is  made,  usually  a  horizontal  projection  of  the  crystal  with  some 
selected  zone  vertical  such  as  is  described  p.  6. 

The  Goniometer. 

Among  "one-circle"  goniometers  one  of  the  best  and  simplest  is 
the  Fuessf  (4,  A)  shown*  in  Fig.  218. 

*  For  a  more  complete  description  of  the  same  course  see  A.  J.  Moses,  in  the 
School  of  Mines  Quarterly,  Vol.  XXVII,  July,  1906,  p.  432. 

f  R.  Fuess,  Steglitz,  near  Berlin,  marks  260,  or  about  65  dollars. 

•  82 


GEOMETRICAL    CONSTANTS    OF  A    CRYSTAL.  83 

The  axes  of  the  two  telescopes,  C  and  T,  are  in  the  same  hori- 
zontal plane  and  intersect  in  the  axis  of  rotation. 

Before  the  objective  of  the  observation  telescope  T  is  an  extra 
lens  which  brings  the  crystal  into  focus.  When  it  is  raised  the 
telescope  is  focused  through  the  collimator,  upon  the  light. 

The  crystal  carrier,  shown  between  the  telescopes,  includes 
three  motions  in  straight  lines  at  right  angles  to  each  other  (by 
the  axis  and  the  slides  n  and  0)  and  two  tipping  motions  on  circular 
arcs  at  right  angles.  The  crystal  is  attached  by  wax  at  p  and  the 
desired  edge*  made  coincident  with  the  axis  of  rotation. 

FIG.  218. 


The  Measuring. 

The  telescope  T  is  set  at  100  to  120  degrees  to  the  collimator  C, 
the  graduated  circle  and  crystal  are  turned  together  by  the 
wheel/,  Fig.  218,  until  the  reflected  signal,  Fig.  219,  is  seen  through 
the  telescope,  the  screw  a  is  tightened,  the  fine  adjustment  made 
by  the  tangent  screw  F,  and  the  vernier  read. 

The  screw  a  is  again  loosened  and  the  rotation  continued  until 
the  signal,  Fig.  219,  is  received  from  a  second  face;  this  is  centered 

*  With  small  ciystals  all  the  angles  of  a  zone  may  be  measured  with  one  adjust- 
ment. 


84  CRYSTALLOGRAPHY. 

by  F  and  a  and  recorded  as  before.     The  difference  between  the  two 
readings  is  the  supplement  angle*  between  the  faces. 

The  best  order  of  measurement,  methods  of  recording,  averaging 
of  corresponding  angles,  adjustments  of  apparatus,  and  other 
details  are  given  in  the  more  complete  descriptions. 

FIG.  219.  FIG.  220. 

^ 


\       x-/*TN         I 

*         ^'  .'  **. 


II.     THE    STEREOGRAPHIC   PROJECTIONf   OR   STEREOGRAM. 
That  is  {he  projection  of  an  imaginary  surrounding  sphere  upon 
its  equatorial  plane  by  lines  drawn  to  its  south  pole. 

The  crystal  is  assumed  to  be  surrounded  by  a  sphere,  the  centers  of  the  sphere 
and  the  crystal  coinciding,  and  radii  to  be  drawn  from  the  center  perpendicular  to 
each  face  of  the  crystal.  From  the  point  P  where  any  such  radius  cuts  the  surface 
of  the  sphere  (called  the  pole  of  the  corresponding  face)  a  line,  Fig.  221,  is  supposed 
to  be  drawn  to  the  south  pole  S,  and  the  point  P'  where  this  line  pierces  the  equatorial 
plane  is  the  stereographic  projection  of  the  face. 

The  method  of  projection  varies  with  the  face.  A  very  brief 
outline  would  be  as  follows: 

Select  the  plane  of  projection,  usually  perpendicular  to  a  zone 
of  prominent  or  numerous  faces,  or  to  an  apparent  axis.  Draw 
a  circle  of  any  convenient  diameter,  and  let  the  point  B,  Fig.  222, 
be  taken  as  the  pole  of  a  chosen  vertical  face. 

*  Because  under  the  conditions  stated  both  telescopes  are  fixed  in  directions,  say 
OC  and  TO,  Fig.  220. 

If  ON  and  ON'  are  the  normals  to  the  two  crystal  faces  NON'  will  be  the  supple- 
ment angle  between  the  faces.  The  two  reflections  will  occur  when  ON  and  ON' 
respectively  bisect  COT.  The  difference  in  rotation  to  these  positions  being  NONr. 

t  By  this  method  vertical  zone-circles  project  as  diameters,  oblique  zone  circles 
as  circles,  each  passing  through  both  ends  of  a  diameter  and  face-poles  project  as 
points  Small  circles  also  project  as  circles.  The  entire  projection  is  called  a 
"stereogram." 

The  zonal  relations  and  the  spherical  triangles  are  therefore  all  represented;  and 
can  be  graphically  solved  or  calculated. 


GEOMETRICAL    CONSTANTS    OF  A    CRYSTAL.  85 

FIG.  221. 


Perspective  of  a  Stereographic  Projection. 

Projecting  the  Vertical  Faces. 

Measure  the  supplement  angles  between  this  face  and  any 
other  vertical  face  L  and  lay  off  the  corresponding  arc  BL  upon 
the  circumference,  thus  determining  the  projection  of  L. 

Projecting  Oblique  Faces  on  Known  Diameters. 

If  any  oblique  face  lies  in  a  zone  with  a  horizontal  and  a  vertical 
face  its  projection  is  on  the  diameter  through  the  vertical  face. 

If  the  face  makes  equal  angles  with  any  two  vertical  faces,  its 
projection  is  on  the  diameter  midway  between  the  diameters 
through  the  projections  of  the  two  vertical  faces. 

In  either  case  the  distance  of  the  desired  projection  from  the 
center  may  be  found  by  laying  off  CD,  Fig.  222,  equal  to  the  angle 
with  the  horizontal  face  (or  BD  equal  the  angle  with  the  vertical 
face  of  the  same  zone)  and  drawing  DS.  Then  is  OR  the  desired 
distance,*  and  is  laid  off  upon  the  proper  diameter  (in  this  case 
on  BB). 

*  The  distance  may  be  laid  off  by  a  protractor,  devised  by  Professor  Penfield,  in 
which  the  values  of  the  stereographically  projected  degrees  have  been  determined 
for  a  circle  of  convenient  size. 


86 


CR  YSTALLOGRAPHY. 


Projecting  Oblique  Faces  on  Known  Oblique  Zones. 

If  during  measurement  an  oblique  face  is  found  to  lie  in  an 
oblique  zone  with  three  (or  even  two)*  already  projected  faces, 
the  circle  drawn  through  these  three  points  is  the  zone  circle 
upon  which  the  desired  projection  lies.f 

FlG.    222. 


In  Fig.  222  let  BPB  be  such  a  circle  and  Q  a  face  in  the  same 
zone,  then  to  project  Q.  Draw  the  diameter  CS  at  90°  to  BB, 
draw  BZ  through  X  the  intersection  of  CS  with  the_zone  circle. 
Find  Y  a  quadrant's  distance  from  Z  and  draw  YB,  its  inter- 
section with  CS  is  F  the  projection  of  the  "pole  of  the  zone." 

Then  'measure  the  angle  between  the  oblique  face  Q  and  any 
known  face  P  of  the  zone.  Draw  a  line  from  F  through  the  known 
face  (P),  prolong  it,  cutting  the  circumference  at  7,  lay  off  JK 
equal  to  the  supplement  angle  between  the  faces  P  and  Q  and 
draw  KF,  intersecting  the  zone  in  the  desired  projection  of  Q. 
Projecting  an  Oblique  Face  not  in  a  Known  Zone. 

This  involves  angles  between  the  unknown  face  and  two  (or 
three)  known  faces.  Preferably  these  are  vertical  faces  or  the 

*  Problem  4,  p.  23,  Characters  of  Crystals,  by  A.  J.  Moses. 

t  The  Penfield  stereographic  protractors  include  a  protractor  of  celluloid  with 
projected  semicircles  for  each  degree  by  which  the  corresponding  radius  may  be 
determined  and  another  protractor  by  which  any  angle  may  be  laid  off  on  any 
oblique  zone. 


GEOMETRICAL    CONSTANTS    OF  A    CRYSTAL.  87 

horizontal  face.  The  projection  then'  involves  the  drawing  of 
projected  small  vertical  and  horizontal  circles.  Failing  these 
oblique  small  circles  must  be  drawn.* 

in.     DETERMINATION    OF    THE    SYMMETRY    AND    THE    ELEMENTAL 

FACES. 

Determining  the  Symmetry.f 

This  can  usually  be  determined  by  two  tests  directly  from  the 
stereographic  projection. 

1.  If  by  revolving  a  tracing  of  the  projection  on  the  projection 
itself  about  the  coincident  centers,  all  the  poles  of  the  tracing 
coincide  with  those  of  the  projection  more  than  once  in  a  complete 
revolution,  then  an  axis  of  two-fold,  three-fold,  four-fold  or  six- 
fold symmetry  exists  in  the  crystal  perpendicular  to  the  plane  of 
projection. 

2.  If  by  folding  the  paper  tracing  on  any  diameter,  all  the  poles 
of  the  one  half  cover  those  of  the  other,  then  this  diameter  is 
the  trace  of  a  plane  of  symmetry  perpendicular  to  the  plane  of 
projection. 

The  following  table  will  identify  the  "system"  unless  a  very 
unimportant  zone  has  been  chosen  as  the  vertical  zone. 

Symmetry  Diameters 

of  Center.  of  Symmetry.  System. 

Six-fold  Six  or  none  Hexagonal 

Four-fold  Four,  two  or  more  Isometric  or  Tetragonal 

Three-fold  Three  or  none  Hexagonal  or  Isometric 

Two-fold  Two  or  none  Isometric  or  Orthorhombic 

Two-fold  None  Monoclinic 

None  One  Monoclinic 

None  None  Triclinic 

The  isometric  crystal  will  always  yield  the  same  projection  for 
some  other  position,  also  in  projections  of  isometric  crystals  there 
are  three  points  90°  apart  which  are  surrounded  by  the  same  group- 
ing of  planes.  In  tetragonal  projections  there  are  two  such 
points. 

*  Explained  in  detail  in  School  of  Mines  Quarterly,  Vol.  27,  p.  441. 

t  This  is  tentative,  other  crystals  of  the  same  substance  may  reveal  faces  which 
lower  the  symmetry.  Indeed  the  true  symmetry  of  a  crystal  is  known  only  when 
all  the  characters  have  been  considered.  Structurally  equivalent  directions  not  only 
imply  similar  groupings  of  bounding  faces  but  physical  identity  in  all  respects. 


88 


CR  YSTALLOGRAPHY. 


Choosing  Elementary  Faces. 

The  three  axial  planes  (100),  (oio)  and  (ooi)  and  the  "para- 
metral"  plane  (in)  are  essential  to  the  determination  of  axes, 
parameters  and  indices. 

The  axial  planes  are  each  parallel  to  two  crystal  axes  (or  con- 
versely the  crystal  axes  are  parallel  to  their  intersection),  their 
choice  therefore  is  dependent  on  the  symmetry. 

If  any  (hkl)  face  occurs  it  may  be  chosen  as  (in)  or  lacking 
such  a  face  any  two  of  (okl),  (hoi),  (hko)  may  be  chosen  as  (on), 
(101)  or  (no)  and  from  these  the  position  of  (in)  be  found. 

IV.     ZONAL   AND    GRAPHIC    DETERMINATION"  OF   INDICES. 

Zonal  "  Indices." 

All  edges  of  a  zone  are  parallel.  Their  common  direction  is 
called  the  zone^xis.  There  must  be  a  radius  in  a  spherical  pro- 
jection parallel  to  each  zone 
axis,  and  this  radius  is  known  if 
the  indices  of  the  point  at  which 
it  cuts  the  sphere  are  known. 
These  three  numbers  are  called 
zone  indices  and  may  be  derived 
from  the  indices  of  any  two 
faces  of  the  zone*  by  cross  mul-  905 
tiplication  and  subtraction  of  f 
the  twice  written  indices  (strik- 
ing off  end  terms  and  reading 
down  alternately  from  left  to  100 
right  and  from  right  to  left). 

For  instance,  in  Fig.  223,  a  zone  with  i  =  (133)  and  g  =  (311), 
the  values  of  the  zone  indices  [uvw]  are  obtained  as  follows: 


FIG.  223. 


010 


30 


3313 
XXX 

1131 


u  =  3  -  3  =  o 

v  =  9  —  i  =8  or  [uvw]  =  [088]  =  [on] 

w  =  i  —  9  =  8 


Face  in  Two  Zones. 

The  indices  of  a  face  in  two  zones  result  from  a  similar  cross 
multiplication  of  the  two  sets  of  zone  indices.  For  instance, 
if  a  face  h,  Fig.  223,  lie  in  the  zone  of  i  =  (133)  and  g  =  (311)  for 

*  Miller's  Treatise  on  Crystallography,  1839,  pp.  7.  8  and  10. 


GEOMETRICAL    CONSTANTS    OF  A    CRYSTAL.  89 

which  the  zone  indices  are  [oil]  and  also  in  the  zone  of  b  =  (335) 
and  c  =  (395)  for  which  similarly  the  zone  indices  are  [503],  the 
values  of  (hkl)  the  indices  of  the  face  h  are  (355)  for 


XXX 
1     3     5     < 


h  =  3  —  o 

k  =  5  ~  o  or  (hkl)  =  (355) 

I  =o  +5 


Various  special  and  more  rapid  methods  of  utilizing  zone  indices 
exist,  for  instance,  In  any  zone  passing  through  two  of  (ooi),  (oio), 
(100).  Every  face  in  the  zone  will  have  that  index  zero  which  is  zero 
in  both.  That  is: 

For  zone  (ooi),  (oio)  the  type  symbol  is  (okl), 
"  "  (ooi),  (100)  "  "  "  "  (hoi), 
11  "  (oio),  (100)  "  "  "  "  (hko). 

Even  more  useful  is  the  determination  of  symbols  by  zones  through 
one  of  (ooi),  (oio)  or  (100). 

The  ratio  of  the  two  indices,  which  are  zero  for  (ooi),  (oio),  or  (100), 
is  constant  for  all  faces  of  the  zone.  Hence: 

Zones  through  (ooi)  h/k  constant, 

"        (oio)  A//         "       , 

(100)  k/l         "       . 

If  then  an  unknown  face  lie  at  the  intersection  of  two  such  zones 
and  the  indices  of  one  face  in  each  zone  are  known  the  indices  of 
the  unknown  face  become  known. 

For  instance,  Fig.  223,  the  same  unknown  face  h  lies  in  a  zone 
with  (oio)  and  (305)  and  also  in  a  zone  with  (100)  and  (in). 

To  substitute  in  hkl  we  have  therefore 

From  first  zone,       3,  -,  5, 
From  second  zone,  — ,  I,  i. 

Remembering  these  are  ratios  and  combining  by  inspection,  the 
indices  of  the  face  h  must  be  (355).  Similarly  the  indices  of  the 
face  b  must  be  (335)  and  of  k  must  be  (on)  and  e  (131),  ^tc. 

Graphical  Determinations  of  Indices. 

It  will  usually  happen  that  only  the  indices  of  a  few  faces  can 
be  obtained  directly  by  zonal  equations,  certain  factors  being 


CR  YSTALLOGRAPHY. 


lacking.  Simple  graphical  constructions  can  be  made  which 
will  give  a  fresh  start. 

The  devices  are  numerous  and  one  such  is  briefly  described.* 
To  Find  the  Indices  of  P  =  hkl. 

The  methods  vary  a  little  with  the  system.     Two  of  the  three 

relations-,  7  and  7  need  to  be  determined,  for  instance: 
K     I  I 

(a)  Finding  -  from  (no)  and  the  corresponding  (hko) . 

Find  T,  Fig.  224,  the  intersection  of  the  radius  through  no 
and  the  tangent  at  100.  Take  RT  parallel  to  CA  as  unity. 


FIG.  224. 

OKI Oil  R       010 


FIG.  225. 


Then  the  radius  through  (hko)  will  cut  this  line  RT  at  a  point 
T  such  that 

h  (  \    first  index       3  . 

RT  =  7     or  RT'  =  ^~T~  =     in  Fig.  224. 

k  \  )  second  index     2 


(b)  Finding  -j  from  on  and  the  corresponding  okl. 

Graphically  or  from  the  records  of  measurements  determine 
the  angle  (ooi)  A  (on).  For  convenience  lay  this  off  in 
the  fourth  quadrant  as  A'E,  Fig.  225,  and  find  T  the  inter- 

*  These  graphic  solutions  were  described  by  A.  J.  Moses  and  A.  F.  Rogers  in 
School  of  Mines  Quarterly,  Vol.  24,  pp.  11-22. 


GEOMETRICAL    CONSTANTS    OF  A    CRYSTAL.  91 

section  of  the  corresponding  radius  with  the  tangent  at  B.  Take 
RT  parallel  CB  as  unity.  Similarly  measure  the  angle  ooi  A  okl, 
lay  this  off  from  A'  as  A'D  and  find  the  intersection  T',  Fig.  225, 
of  the  corresponding  radius  with  RT,  then 

k       I 
RT  =  -j  =  -in  Fig.  225. 

The  same  angles  are  used  in  Fig.  225  as  in  Fig.  224;  hence  com- 
bining by  inspection  with  -  =  T  we  have 

rf-  /V 


-,  I,  2, 

that  is  324  satisfies  both,  hence  P  =  (hkl)  =  (324). 

V.     THE   CALCULATION   OF   AXIAL   ELEMENTS. 

Simple  formulae  in  terms  of  the  indices  and  interfacial  angles 
are  most  used.  For  the  fairest  average  every  available  measured 
angle  should  have  due  weight.  Considering  the  systems  in  order: 

The  Isometric  System. 

In  this  system  the  parameters  are  equal  and  the  angles  between 
the  axes  are  right  angles. 

The  Tetragonal  System. 

Taking  the  parameter  a  =  I  the  only  axial  element  is  c. 

The  formulae  of  the  orthorhombic  apply  if  a  is  made  equal  unity 

(a  =  i). 

The  Orthorhombic  System. 

Taking  the  parameter  6  =  I  the  axial  elements  are  a  and  c. 
The  simplest  formulae  are: 

a  =  -  tan  (100)  A  (hko)',  c  =  -  tan  (ooi)  A  (ofe/). 

K  K 

Similar  but  somewhat  more  complex  formulae  exist  for  the  (hkl) 
angles. 

The  Hexagonal  System. 

Taking  the  parameter  a  •  =  I  the  only  axial  element  is  c. 


92  CRYSTALLOGRAPHY. 

The  simplest  formulae  for  this  are 

c  =  T  cos  30°  tan  (oooi)  A  (kohl) 

= —tan  (oooi)  A  (hh2hl). 

The  Monoclinic  System. 

Taking  the  parameter  b  as  unity  the  axial  elements  are  the 
values  of  a  and  c  and  of  the  acute  angle  (3  between  the  vertical 
and  clino  axes. 

0  =  (100)  A  (ooi), 

cos  (ooi)  A  (hko) 
)S  *  =  cos  (oio)  A  (hko)  ' 

The  simplest  formulae  for  d  and  c  are 

h  cot  (oio)  A  (hko) 
=  k~          sin  ft          ~  ' 

I  tan  (ooi)  A  (okl) 
=  k~          sin  ft 
The  Triclinic  System. 

The  axial  elements  are  the  parameters  &,  b  and  c,  in  which  b  is 
taken  as  unity  and  the  angles  between  the  axes  a  =  b  A  c, 
ft  =  a  A  c  and  7  =  6  A  d. 

The  formulae  are  much  more  complex;  for  instance  the  simplest 

is  

a  _      \sm  (S  -  AC)  sin  (S  -  AS) 
1  2  ~  M        sin  5  sin  (5  -  BC) 
in  which 

^1  =  (100),  C  =  (ooi),  5  =  oio  and  5  =  $(AB  +  B.C  +  ^C). 

VI.     CRYSTAL    DRAWING. 

Clinographic  and  orthographic  projections  of  crystals  are  much 
used  in  illustration. 
Clinographic  Projections. 

In  clinographic  drawings  the  crystal  is  projected  upon  a  vertical 
plane  by  parallel  rays  oblique  to  the  plane  of  projection.  The 
eye  is  assumed  at  an  infinite  distance  a  little  to  the  right  and  above 
the  center  of  the  crystal. 


GEOMETRICAL    CONSTANTS    OF  A    CRYSTAL.  93 

The  figures  obtained  in  this  way  have  an  appearance  of  solidity, 
all  parallel  edges  are  parallel  and  all  points  in  a  given  line  remain 
the  same  proportionate  distances  apart. 

The  drawing  consists  chiefly  of  two  stages,  first  finding  the 
"axial  cross"  of  the  crystal,  that  is  the  true  projection  of  the 
crystal  axes  cut  off  at  the  parameter  lengths;  second,  finding  the 
direction  of  the  projection  of  any  edges  from  the  indices  of  the 
intersecting  planes. 

Construction  of  "  Axial  Cross." 

All  axial  crosses  are  derived  from  the  projection  of  three  equal 
lines  at  right  angles,  that  is,  from  the  isometric  axial  cross*  for 
constructing  which  formulae  exist  dependent  on  the  direction  of 
the  line  of  sight. 

For  other  systems  the  necessary  changes!  are  made  in  the 
directions  of  these  isometric  axes  and  then  each  is  changed  in 
length  to  fit  the  parameters  of  the  species. 

Thus  in  a  monoclinic  species  the  an- 

FlG.    226. 

gle  between  the  clino  and  vertical  axes 
being  known  the  projection  of  the  front 
to  back  isometric  axis  is  replaced  by  the 
projection  of  a  line  equal  in  length  to  an 
isometric  axis  but  in  the  direction^  of 
the  desired  clino  axis. 

These  three  lines,  Fig.  226,  are  then 
lengthened  or  shortened  in  the  propor- 
tions given  by  the  parameters  of  the 
species.  If  a  :  b  :  c  =  0.73  : 1  :  1.23,  the 

left  to  right  axis  is  not  changed,  the  vertical  is  made  1.23  times 
its  isometric  length  and  the  front  to  back  axis  0.73  its  isometric 
length  DD. 

*  For  the  drawings  of  this  book  the  projected  isometric  "axial  cross"  consists  of 
three  lines.  OA  :  OB  :  OC  =  37  :  100  :  104,  in  lengths  intersecting  at  a  common 
center  and  with  BOC  =  93°  8',  AOC  =  116°  17'.  See  Fig.  226. 

t  See  A.  J.  Moses,  Characters  of  Crystals,  pp.  79-84. 

t  To  obtain  this  direction  in  perspective  proceed  as  follows:  Upon  the  isometric 
"cross"  layoff  Or  =  OC^cos  ft  and  On  =  OA  sin  ft,  Fig.  226.  Complete  the  parallelo- 
gram OrDn\  then  is  DD  the  projection  of  a  line  equal  in  length  to  an  isometric  axis 
but  in  the  direction  of  the  desired  clino  axis. 


94  CR  YSTALL  O  GRAPHY. 

Determination  of  the  Direction  of  Edges.* 

The  unit  form  is  obtained  by  joining  the  extremities  of  the  axial 
cross  by  straight  lines,  and  other  simple  forms  are  easily  drawn 
by  methods  which  suggest  themselves. 

The  projection  of  the  edge  between  any 
two  planes  may  be  derived  from  the  re- 
ciprocals of  the  Miller  indices  or  the  Weiss 
coefficients  as  follows: 

For  instance  in    Fig.  227  let  OA,  OB, 
OC  be  one  half   of   any  projected    axial     A    y.-'** 
cross  and  the  problem  be  to  find  the  pro- 
jection of  the  edge  between  two  planes  for  which  the  symbols  are: 

The  dome     oo  a  :  b  :  \c  or  (041), 

_ 
The  prism         a  :  b  :  ooc  or  (no). 

The  respective  Weiss  coefficients  or  reciprocal  Miller  indices  are 
oo  :  i  :  4,  and  I  :  I  :  oo . 

Dividing  each  by  the  third  term,  which  is  equivalent  to  moving  each 
face  parallel  to  itself  until  it  cuts  c  at  its  parametral  value  OC, 

The  dome      oo  :  J4  :  i ;  The  prism     o  :  o  :  I . 

The  traces  of  these  planes  on  AOB  are  respectively  YY  and  OS. 
These  traces  intersect  at  5. 

The  two  planes  have  therefore  one  point  in  common  at  S  and 
one  at  C,  hence  the  desired  projected  edge*  is  parallel  SC. 

All  other  intersections  may  be  obtained  in  the  same  manner  on 
the  axial  cross. 

Construction  of  the  Figure. 

Generally  the  principal  forms  are  drawn  first  and  the  minor 
modifying  planes  later,  either  in  ideal  symmetry  or  so  as  to  indicate 
the  relative  development  of  faces  and  forms. 

A  second  axial  cross  may  be  drawn  parallel  to  that  used  in 
determining  the  edge  directions  and  these  may  be  transferred 
by  triangles. 

*  Prismatic  traces,  such  as  OS  for  (no),  involve  considering  the  trace  of  the 
corresponding  pyramid,  that  is,  o  :  o  :  i  means  a  line  OS  through  the  centre  parallel 
to  AB  (not  drawn),  the  trace  of  the  pyramid  (in). 


GEOMETRICAL    CONSTANTS   OF  A    CRYSTAL.  95 

Orthographic  Projections.     (See  Figs.  6  to  10.) 

The  projection  upon  a  plane  by  lines  perpendicular  to  that 
plane.  Usually  a  prominent  zone  is  placed  perpendicular  to  the 
plane  of  projection  and  its  faces  appear  as  lines  inclined  to  each 
other  at  their  true  values. 

The  Projection  of  Oblique  Edges  is  very  much  as  in  clino- 
graphic  projection.  If,  as  is  usual,  the  plane  of  projection  is  the 
plane  of  two  crystal  axes  then  the  projection  of  any  oblique  edge  is 
obtained  by  drawing  the  axes,  and  finding  the  traces  of  each  plane 
by  laying  off  on  these  axes  the  proper  intercepts.*  The  inter- 
section of  any  two  traces  is  a  point  of  the  edge,  the  intersection  of 
the  two  axes  is  another. 

If  a  stereographic  projection  upon  the  same  plane  has  been 
made  the  tangent  to  the  outer  circle  at  the  point  where  it  is  cut  by 
the  zone  of  the  two  planes  is  the  direction  of  their  edge. 

*  As  in  clinographic  projection,  the  intercepts  are  reduced  so  that  the  third  term 
is  unity. 


CHAPTER  X. 
CRYSTALLO-OPTICS. 

Light,  the  agent  which  by  its  action  on  the  retina  produces  the 
sensation  of  vision,  is  transmitted  in  any  homogeneous  medium 
in  straight  lines  which  may  be  called  light  rays. 

There  is  a  vibration,  or  a  waxing  and  waning  of  force,  at  right 
angles  to  the  direction  of  transmission  which  may  be  designated 
in  direction  and  intensity  by  a  straight  line  at  right  angles  to 
the  direction  of  advance  and  may  for  convenience  be  called  a 
vibration. 

In  common  light  these  "vibrations"  may  be  thought  of  as 
constantly  altering  in  direction  though  always  in  the  same  plane 
and  changing  so  rapidly  that  the  effect  during  the  period  of  a 
distinct  impression  upon  the  retina  is  an  average  of  many. 

It  is  possible,  however,  by  certain  methods  later  to  be  explained 
to  reduce  these  vibrations  of  many  orientations  to  one  direction, 
that  is,  to  "polarize"  com- 
mon light. 

Reflection. 

Rays  of  light  falling  on  a 
polished  surface  are  reflected 
and  follow  two  laws. 

1.  The  angle  of   incidence 
is    equal  to  the  angle  of  re- 
flection. 

2.  Both  rays  are  in  the  same 
plane  perpendicular  to  the  re- 
flecting surface. 

Let  MM',  Fig.  228,  be  a 
section  of  a  mirror.  The 

hand  at  O  appears  to  be  seen  at  0'  by  the  eye  at  £,  the  line  00' 
being  perpendicular  to  the  mirror  and  bisected  by  it.  The  an- 
gles i  and  if  are  equal. 

96 


CRYSTALLO-OPTICS.  97 

Refraction. 

Rays  of  light  in  passing  obliquely  from  one  medium  to  another 
in  which  the  velocity  of  transmission  is  different  are  bent  or 
refracted.  If  the  velocity  is  lessened  the  bending  is  towards  the 
perpendicular  to  the  surface  of  contact,  if  the  velocity  is  increased 
the  bending  is  away  from  the  perpendicular.  Thus  in  Fig.  229 
let  AB  represent  the  surface  of  contact  and  let  the  light  velocity 
be  slower  in  the  lower  medium.  Any  ray  of  light  CO  on  entering 
this  medium  is  bent  towards  the  perpendicular  ON  and  follows 
a  path  such  as  OD,  similarly  C'O  follows  OD> '. 

Conversely  if  the  light  travels  in  the  opposite  direction,  on 
reaching  AB  the  rays  would  be  bent  from  the  perpendicular  ON. 

Index  of  Refraction. 

It  has  been  proved  that  whatever  the  angle  of  incidence,  the 
ratio  of  the  sines  of  the  angles  of  incidence  and  the  angle  of  refrac- 
tion is  constant  for  the  same  two  media  and  equal  to  the  ratio  of 
the  velocities  of  the  incident  and  the  refracted  ray.  That  is, 

sin  i       Vi 
n  =  ~.       =  "TT  . 
sin  r       V2 

sin  i        ab    , 

Thus  in  Fig.  230  the  ratio  -7—  or  —    is  equal  to  the   ratio 

sin  r        cd 

sin  V       a'V 

~ /  or  "717  •     This  constant  ratio   for  any  two  media  is  called 

sin  r'       c'd' 

the  index  of  refraction  of  the  second  medium  with  respect  to  the 
first.  Unless  otherwise  specified  a  stated  index  of  refraction 
assumes  the  first  medium  to  be  air.* 

There  is  no  refraction  with  normal  incidence.  With  a  plane- 
parallel  plate  the  ray  emerging  at  the  second  surface  is  parallel 
to  the  ray  entering  at  the  first  surface. 

If  the  indices  of  refraction  of  two  media  with  respect  to  air 
are  known  the  direction  of  any  ray  after  bending  may  be  found 
by  drawing  concentric  circles  as  in  Fig.  230  with  radii  correspond- 
ing to  these  indices.  In  the  circle  corresponding  to  the  first 
medium  a  diameter  is  drawn  parallel  to  the  incident  ray.  From 
its  end  T  (or  T'),  Fig.  230,  a  line  perpendicular  to  the  surface  is 

*  The  absolute  index  of  refraction  assumes  Vi  to  be  the  velocity  of  light  in  a 
vacuum. 


98 


CR  YSTALLOGRAPHY. 


drawn,  the  point  c  (or  c')  where  it  cuts  the  second  circle  is  a  point 
of  the  refracted  ray  OD  (or  OD'). 
Total  Reflection. 

If  the  angle  of  refraction  is  greater  than  the  angle  of  incidence, 
as  is  the  case  when  light  travels  faster  in  the  second  medium, 


FIG.  229. 


FIG.  230. 


V  V 


there  is  a  so-called  "critical"  angle  of  incidence  for  which  the 
angle  of  refraction  is  90°;  that  is,  the  refracted  ray  travels  along 
the  border  surface.  For  any  angle  of  incidence  greater  than  this 
the  light  is  totally  reflected. 

In  Fig.  231  constructed  on  the  same  values  as  Figs.  229  and  230 
rays  like  DO  and  D'O  follow  paths  OC  and  OC'  in  the  second 
medium,  but  some  ray  10  at  the  critical  angle  Z  follows  the  path 
OB.  All  rays  incident  at  greater  angles  than  Z,  such  as  MO,  fail 
utterly  to  penetrate  the  second  medium  and  are  totally  reflected 
as  along  OP. 

The  value  of  the  critical  angle  is  easily  found  from  the  indices 
of  refraction  of  the  two  media,  let  n  be  that  of  the  first,  and  n' 
that  of  the  second,  then  n  sin  i  =  n'  sin  r,  but  if  r  is  90°  sin  r  =  I, 

that  is,  n  sin  i  =  n'  or  sin  i  =  —  .     If  the  second  medium  is  air 

n 

n'  =  i  and  the  index  of  refraction  of  the  first  medium  is  n  =  - 

sin  ^ 

Dispersion. 

When  white  light  passes  obliquely  from  oae  medium  into  an- 

*  The  ray  at  the  critical  angle  is  found  graphically  by  drawing  a  tangent  at  x, 
Fig.  230,  thus  finding  y  a  point  of  the  desired  diameter. 


CR  YSTALL  O-  OPTICS.  99 

other,  it  is  decomposed  into  a  spectrum  consisting  of  many  kinds 
of  light  which  are  differently  colored.* 

These  component  so-called  monochromatic  lights  have  each  a 
different  wave-length!  which  can  be  closely  calculated.  For  in- 
stance, in  million ths  of  a  millimeter  some  prominent  colors  are: 
Violet  Hj  393.3,  Blue  FI  486,  Green  E  526.9,  Yellow  Dx  589.5, 
Red  C  656.2,  Red  A  760.4. 

With  nearly  all  substances  the  shorter  the  wave-length  the 
greater  the  refraction  of  the  light,  that  is,  the  violet  is  most  bent, 
the  red  least.  It  follows  therefore  that  indices  of  refraction  differ 
with  the  light  used  and  should  be  obtained  with  monochromatic 
light. 

OPTICAL   GROUPS. 

According  to  their  optical  symmetry  crystals  may  be  classified 
as: 

I  so  tropic.     Isometric. 

Anisotropic,  Uniaxial.     Hexagonal  and  tetragonal. 

Anisotropic,  Biaxial.     Orthrohombic,  monoclinic,  and  triclinic. 

THE    OPTICALLY   ISOTROPIC    CRYSTALS. 

Any  normal  isometric  crystal  shows  the  same  optical  properties 
in  all  directions,  and  is  therefore  optically  isotropic. J 

Ignoring  a  few  salts  which  crystallize  in  class  28,  p.  66,  and 
are  circularly  polarizing  in  all  directions  the  following  statements, 
hold: 

The  Index  of  Refraction  of  any  isometric  crystal  is  a  constant 
for  all  directions  of  transmission. 

Absorption  increases  with  the  thickness  and  may  be  selective, 
giving  color,  but  in  any  one  crystal  equal  thicknesses  in  different 
directions  give  equal  absorption  and  the  same  color  tint. 

That  is,  the  optical  tests  on  isotropic  crystals  are  limited  to 
color,  index  of  refraction  and  absence  of  double  refraction. 

*  With  plane  parallel  plates  the  light  emerging  from  the  second  surface  is  parallel 
to  the  entering  light  and  the  color  is  not  noticed.  With  a  prism  of  proper 
angles  the  divergence  is  increased  at  the  second  surface  of  contact  and  a  spectrum 
obtained. 

t  The  distance  light  advances  during  a  complete  vibration  is  called  its  wave-length. 

t  Isotropic  media  behave  alike  in  all  directions  with  regard  to  light  phenomena. 
Most  liquids  and  glasses  are  isotropic. 


100 


CR  YSTALLOGRAPHY. 


THE    GENERAL   PROPERTIES    OF   ANISOTROPIC    CRYSTALS. 

Ahisotropic  media  do  not  behave  alike  in  all  directions. 

As  all  crystals  except  those  of  the  isometric  system  show 
different  optical  behavior  in  directions  not  parallel  they  are  said 
to  be  optically  anisotropic. 

All  anisotropic  minerals  are  doubly  refracting  in  most  directions 
but  possess  either  one  or  two  directions  of  single  refraction  known 
as  optic  axes. 

DOUBLE   REFRACTION   AND    POLARIZATION   IN    CALCITE. 

That  a  ray  of  ordinary  light  entering  calcite  emerges  as  two 
rays  of  polarized  light  may  be  demonstrated  as  follows : 

A  moderately  thick  calcite*  cleavage,  Fig.  232,  is  mounted  with 
a  rhombic  face  vertical  and  so  that  it  can  be  revolved  about  a 
horizontal  axis  perpendicular  to  this  face,  Fig.  233. 

A  horizontal  ray  of  light,  IT,  Fig.  234,  is  allowed  to  fall  upon 
the  vertical  face.  It  passes  through. the  calcite  and  emerges  as 
two  rays,  one,  TO,  undiverted  from  its  course,  as  would  happen 
with  ordinary  refraction  and  perpendicular  incidence,  while  the 
other,  TE,  has  undergone  some  "extraordinary"  refraction.  On 


FIG.  232. 


FIG.  233. 


FIG.  234. 


revolution  of  the  calcite  the  diverted  or  extraordinary  ray,  TE, 
appears  to  revolve  around  the  ordinary  ray,  TO,  at  a  fixed  distance 

*  Double  refraction  in  calcite  was  described  in  1670  by  Erasmus  Bartholin,  of 
Copenhagen,  one  year  after  Steno's  announcement  of  the  constancy  of  corresponding 
angles  in  quartz.  That  all  its  optical  behavior  corresponded  to  a  double  shelled 
ray  surface  was  discovered  by  Huyghens  in  1678. 


CR  YSTALL  O-  OPTICS.  I  o  I 

from  it  and  both  evidently  remain  in  a  plane  parallel  to  the  plane 
abed  through  the  short-diagonal,  Fig.  232. 

The  two  rays  also  appear  to  be  of  approximately  equal  bright- 
ness and  not  to  change  during  the  revolution  of  the  calcite. 
Proof  that  the  Rays  are  not  Common  Light. 

If  the  two  rays  TO  and  TE  are  common  light  then  by  shutting 
off  one  and  allowing  the  other  to  go  through  a  second  calcite 
rhomb  mounted  like  the  first  there  should  again  result  two  rays 
of  essentially  equal  brightness  for  all  stages  of  rotation  of  the  calcite 
rhomb.  This  however  is  not  the  case. 

If  TO,  the  ordinary  ray,  is  used  as  a  source,  then,  when  the  short 
diagonals  of  the  vertical  faces  of  the  two  calcite  rhombs  are 
parallel  only  an  ordinary  ray  is  seen,  when  they  are  crossed  only 
an  extraordinary,  between  these  positions  there  are  always  two 
rays  which  alternately  wax  and  wane  and  are  only  equal  when 
the  short  diagonals  are  at  45°  to  each  other. 

Also  if  TE,  the  extraordinary  ray,  is  used  as  a  source  there  is  a 
similar  series  of  results,  but  the  relative  positions  of  the  two 
calcites  for  any  particular  result  have  changed  by  90°.  That  is, 
an  ordinary  ray  is  seen  when  the  short  diagonals  are  crossed,  and 
an  extraordinary  ray  when  they  are  parallel  and  for  any  inter- 
mediate position,  the  intensities  of  the  two  rays  have  been  reversed. 

The  rays  TO  and  TE  therefore  differ  from  common  light  and 
differ  from  each  other  by  some  90°  relation. 

Transmission  in  other  directions  in  calcite  gives  similar  results, 
but  with  this  difference,  that  for  the  same  thickness  the  divergence 
of  10  and  IE  differs  from  a  maximum  for  transmission  at  right 
angles  to  the  three-fold  symmetry  axis  to  zero  for  transmission 
parallel  to  it. 

Theory  to  Explain  Double  Refraction  of  Calcite. 

The  few  facts  stated  show  that  the  results  depend  upon  the 
crystal  structure  of  the  calcite.  If  it  is  assumed  that  this  structure 
is  such  that  the  vibrations  of  any  entering  ray*  are  converted 

*  The  different  effects  of  the  same  structure  on  common  light  and  on  a  ray  from 
the  first  calcite  fit  in  with  this  theory.  For  the  rapidly  changing  orientation  of  the 
vibrations  in  common  light  yield  rapidly  changing  components  and  an  average 
essentially  equal  "brightness"  for  the  two  rays  for  all  positions,  whereas  the  fixed 
vibration  direction  of  the  "polarized  ray"  yields  varying  components  as  the  relative 
positions  of  the  calcites  change. 


1 02  CR  YSTALL  O  GRAPHY. 

into  two  sets  of  straight-lined  vibrations,  one  parallel  to  abed, 
Fig.  232,  one  at  right  angles  thereto,  all  the  results  of  the  experi- 
ment may  be  graphically  shown  for  different  relative  positions  of 
the  two  calcites  by  representing  these  directions  of  vibration  by 
straight  lines  and  the  intensities  by  the  lengths  of  these  lines. 

Assuming  that  the  vibrations  of  the  extraordinary  ray  are  parallel  abed  and 
that  of  the  ordinary  at  right  angles  thereto,  the  problem  is  simply  to  resolve  the 
initial  ray,  represented  by  a  line  definite  in  length  and  parallel  (or  at  right  angles) 
to  the  short  diagonal  of  the  first  calcite,  into  components  parallel  and  at  right  angles 
to  the  short  diagonal  of  the  second  calcite. 

Double  Refraction  not  Limited  to  Calcite. 

By  other  methods  later  to  be  elaborated  it  may  be  shown 
that  double  refraction  is  a  common  property  of  all  crystals  except 
the  isometric  and  that  the  vibrations  of  any  entering  ray  are 
converted  by  any  crystal  (not  isometric)  into  two  sets  of  straight- 
lined  vibrations  in  planes  at  right  angles  to  each  other,  the  direc- 
tions of  these  planes  being  dependent  on  the  crystal. 

THE    OPTICALLY   UNIAXIAL    CRYSTALS. 

Optic  Axis. 

In  every  crystal  of  the  hexagonal  or  tetragonal  system  the 
direction  of  the  principal  crystallographic  axis  (c)  is  a  direction 
either  of  single  refraction  or  of  circular  polarization  and  the 
directions  equally  inclined  to  the  crystallographic  axis  are  optically 
equivalent. 

The  crystallographic  axis  c  is  therefore  an  Optic  Axis. 

Ray  Surface. 

The  optical  properties  of  a  uniaxial  crystal  are  best  understood 
by  considering  the  shape  of  the  Ray  Surface,*  which  consists  of 
two  shells  with  a  common  center.  One  is  a  sphere,  the  other  an 
ellipsoid  of  revolution,  the  axis  of  revolution  being  either  the 
major  or  minor  axis  of  the  ellipse  but  always  a  diameter  of  the 
sphere.  It  is  also  the  optic  axis. 

Evidently  for  every  direction  except  that  of  the  optic  axis 
two  rays  are  transmitted,  an  ordinary  with  a  velocity  indicated  by 

*  Assume  one  vibration  of  monochromatic  light  within  a  homogeneous  medium 
and  the  transmission  of  this  vibration  in  all  directions  along  rays.  At  the  end  of 
any  period  the  motion  will  have  reached  some  definite  point  on  each  ray.  The  closed 
surface  through  these  points  is  the  ray  surface  of  the  substance. 


CR  YSTALL  O-  OPTICS. 


103 


the  sphere  radius  and  an  extraordinary  with  a  velocity  indicated 
by  the  corresponding  radius  vector  of  the  ellipsoid,  and  the  greatest 
difference  of  velocity  exists  for  the  direction  of  transmission  at 
right  angles  to  the  optic  axis. 

Positive  and  Negative  Character  of  Ray  Surface. 

The  spherical  shell  may  surround  the  ellipsoid  shell  or  vice  versa. 
The  former  combination  is  called  a  positive  ray  surface,  the  latter 
a  negative. 

In  the  positive  ray  surface,  Fig.  235,  the  constant  ordinary 
ray  is  evidently  faster  for  any  directions  of  transmission  than  the 
extraordinary  and  the  slowest  ray  is  evidently  the  extraordinary 
transmitted  at  right  angles  to  the  axis  of  rotation  or  optic  axis. 
In  the  negative  ray  surface,  Fig.  236,  this  is  reversed  and  the 


Section  of  Positive  Ray  Surface. 


Section  of  Negative  Ray  Surface. 


fastest  ray  is  the  extraordinary  ray  transmitted  at  right  angles  to 
the  optic  axis. 

If  the  direction  of  vibration  of  the  fastest  and  slowest  rays  be 
denoted  respectively  by  X  and  Z  then,  as  indicated  in  the  ray 
surfaces, 

Z  is  the  axis  of  rotation  or  optic  axis  in  a  positive  ray  surface 
and  X  in  a  negative. 

Or  since  the  optic  axis  is  the  crystallographic  axis  c  we  may 
summarize : 

+  when  Z  parallel  c, 

-      "     X       "       c. 
Indices  of  Refraction. 

From  what  has  just  been  said  it  follows  that  for  any  direction  of 
transmission  there  is  one  constant  index  of  refraction  and  for 


104  CR  YSTALL  OGRAPHY- 

any  direction  but  the  optic  axis  there  is  a  second  index  varying  with 
the  direction.  Finally  that  the  indices  of  refraction  obtained  for 
a  direction  at  right  angles  to  the  optic  axis  are  the  largest  and 
smallest  obtainable  and  are  called  the  principal  indices. 

The  principal  indices  are  most  conveniently,  and  in  conformity  with  the  usage  in 
biaxial  crystals,  denoted  by  7  and  a,  y,  the  largest  index,  is  the  index  of  the 'slowest 
transmitted  ray,  with  vibration  direction  parallel  Z;  a,  the  smallest  index,  is  the 
index  of  the  fastest  transmitted  ray  with  vibration  direction  parallel  X.  Hence  the 
relations  may  also  be  stated:  Positive  when  vibration  of  7  =  c,  Negative  when 
vibration  a.  =  c. 

"  Birefringence  "  and  Phase  Difference. 

The   difference   between    the    principal    indices    is    called    the 
birefringence    or    strength    of    double    refraction.     In    different 
crystals  of  the  same  species  it  is  more  constant  than  the  indices 
themselves.     For  any  direction  except  that  of  the  optic  axis, 
both  rays  are  retarded  but  one  more  than  the  other.     There  must 
therefore  develop  a  phase  difference  increasing  with  the  thickness. 
If  the  direction  is  at  right  angles  to  the  optic  axes 
Phase  difference  =  thickness  X  birefringence  or  A  =  t(y  —  a). 

Vibration  Directions. 

For  any  direction  of  transmission  the  two  rays  will  possess 
definite  directions  of  vibration  at  90°  to  each.  When  these  can 
be  compared  with  a  crystallographic  direction  they  are  useful. 
One  will  always  be  in  the  plane  through  the  optic  axis. 

Circular  Polarization. 

In  quartz  and  cinnabar  crystals  the  light  transmitted  in  the 
direction  of  the  optic  axis  is  "circularly  polarized." 

That  is  ordinary  polarized  rays  with  vibration  in  straight  lines 
in  a  known  plane  emerge  with  their  vibrations  in  a  different  plane. 

The  angle  of  rotation  is  dependent  on  the  thickness  and  for  quartz  amounts  to  24° 
per  millimeter  for  sodium  light. 

A  thin  section  or  fragment  of  basal  quai  tz  of  say  .03  to  .04  mm.  thickness  would 
therefore  develope  less  than  one  degree  of  rotation. 

In  other  directions  these  minerals  behave  nearly,  though  not 
exactly,  like  ordinary  uniaxial  minerals. 

Absorption  and  Pleochroism. 

In  symmetry  if  not  in  degree  the  absorption  phenomena  corre- 
spond to  the  transmission.  The  absorption  of  the  ordinary  ray 


CR  YSTALL  O-  OPTICS.  105 

\ 

being  independent  of  the  direction  of  transmission,  while  that  of 
the  extraordinary  varies  with  the  inclination  to  the  optic  axis, 
but  is  constant  for  the  same  angle  and  differs  most  from  that 
of  the  ordinary  for  transmission  normal  to  the  optic  axis. 

THE    OPTICALLY   BIAXIAL   CRYSTALS. 

Optic  Axis. 

In  orthorhombic,  monoclinic  and  triclinic  crystals,  no  true 
optic  axes  exist  because  there  is  no  direction  of  optical  isotropy. 

There  are,  for  monochromatic  light*  and  constant  temperature, 
two  directions  of  single  refraction,  and  as  in  most  cases  the  uniaxial 
optic  axis  is  a  direction  of  single  refraction  these  by  a  strained 
analogy  are  called  optic  axes,  for  light  of  that  wave-length. 

They  are  determinable  directions  and  therefore  useful  and  their  very  variations 
for  temperature  and  wave-length  constitute  tests. 

The  Biaxial  Ray  Surface. 

For  a  given  temperature  a  monochromatic  light  motion  starting 
from  a  point  within  a  biaxial  crystal  reaches  at  any  moment  a 
very  complicated  double  ray  surface  which  is  symmetrical  only 
to  three  lines  at  right  angles  called  principal  vibration  directions, 
and  three  planes,  each  through  two  of  these  lines,  called  optical 
principal  sections. 

Two  of  the  three  lines  are  always  the  vibration  directions  of  the 
fastest  and  slowest  rays,  the  third  is  at  right  angles  to  these  and 
is  the  vibration  direction  corresponding  to  some  ray  of  intermediate 
velocity. 

It  may  be  noted  that  the  planes  and  axes  of  geometric  symmetry 
are  alwaysf  optical  principal  sections  or  principal  vibration 
directions. 

In  conformity  with  the  convention  of  the  uniaxial  crystals 
let  the  vibration  directions  of  the  fastest  and  slowest  rays  be 

*  The  directions  of  single  refraction  or  so-called  optic  axes  depend  upon  the 
principal  indices  of  refraction,  hence  change  both  with  wave-length  and  temperature, 
the  amount  of  change  varying  from  a  few  minutes  to  many  degrees. 

t  Thus  in  Orthorhombic  Crystals  the  principal  vibration  directions  and  optical 
principal  sections  are  constant  for  all  colors,  in  Monoclinic  Crystals  one  principal 
vibration  direction  and  one  optical  principal  section  are  fixed  for  ail  colors,  the  others 
vary  with  the  wave-length;  in  Triclimc  Crystals  there  are  no  principal  vibration 
directions  or  principal  sections  which  are  constant  for  all  cclors. 


io6 


CR  YSTALLOGRAPHY. 


denoted  by  X  and  Z  respectively  and  let  F  represent  a  direction 
at  right  angles  to  X  and  Z. 

The  shape  of  the  ray  surface  may  be  judged  from  the  shape  of 
the  optical  principal  sections  X  Y,  XZ,  and  YZ. 


Section  XY. 


Section  XZ. 


Section  YZ. 


Optical  Principal  Section  XY,  Fig.  237,  cuts  the  two  shells  of 
the  ray  surface  as  a  circle  within  an  ellipse  with  radius,  major  and 
minor  axes  respectively  slowest,  fastest  and  intermediate  veloci- 
ties.* 

Optical  Principal  Section  YZ,  Fig.  238,  cuts  the  two  shells  of 
the  ray  surface  as  an  ellipse  within  a  circle  with  radius,  major  and 
minor  axes  respectively  fastest,  intermediate  and  slowest  veloci- 
ties. 

The  Optical  Principal  Section  XZ.  This  is  the  most  important 
section  because  it  is  the  plane  of  the  optic  axes.  It  cuts  from  the 
ray  surface  an  ellipse  and  a  circle  which  intersects  the  ellipse  in 
four  symmetrically  placed  points,  £,  Fig.  239.  The  radius,  major 
and  minor  axes  are  respectively  the  intermediate,  fastest  and 
slowest  velocities.! 

Near  but  not  at  the  points  E ;  common  tangent  planes  can  be 
drawn  to  each  shell.  The  directions,  A  A ,  normal  to  these  common 
tangent  planes  are  directions  of  single  refraction,  that  is,  are  the 

*  These  velocities  are  proportionate  to  the  reciprocals  of  a,  /9,  y,  the  indices  of 
refraction  for  rays  with  vibrations  parallel  X,  F  and  Z. 

t  The  light  emerging  on  the  direction  AA  is  not  simply  the  singly  refracted  ray 
which  has  travelled  in  the  crystal  in  the  direction  A  A  but  all  that  diverging  cone  of 
rays  with  0  as  a  point  and  the  circle  of  contact  of  the  tangent  plane  as  a  base.  Each 
ray  has  its  own  direction  of  vibration. 


CR  YSTALL  O-  OPTICS.  1 07 

so-called  optic  axes  and    the  rays  travelling   in  these  directions 
have  the  intermediate  velocity  (or  index  of  refraction  /3). 

Positive  and  Negative  Character  of  Ray  Surface.* 

In  XZ,  the  plane  of  the  optic  axes,  X  and  Z  bisect  the  angles 

between  these  axes.     If  the  acute  bisectrix  is  Z  (Bxa  =  Z),  the 

ray  surface  is  said  to  be  positive.^ 

If  the  acute  bisectrix  is  X  (Bxa  =  X),  the  ray  surface  is  said 

to  be  negative. 

OPTICAL   PROPERTIES   AND    CONSTANTS    OF   BIAXIAL   CRYSTALS. 

These  can  most  simply  be  stated  by  reference  to  the  uniaxial 
crystals. 

Indices  of  Refraction. 

The  principal  indices  are  for  rays  with  vibration  directions 
parallel  the  three  axes  of  symmetry;  one  will  be  7  the  largest 
index  anywhere  obtainable,  one  will  be  a,  the  smallest,  the  third 
will  be  ]8,  that  of  a  ray  with  vibration  directions  at  right  angles  to 
these. 

For  other  directions  intermediate  values  are  obtained.  There 
is  no  constant  index. 

Birefringence. 

The  difference  between  the  largest  and  smallest  index  (7  —  a) 
is  the  birefringence  of  the  crystal. 

Optic  Axial  Angle. 

The  angles  between  the  optic  axes  can  be  measured — the  acute 
angle  is  designated  by  2  V. 

Vibration  Directions. 

As  with  the  uniaxial  these  lead  to  a  knowledge  of  the  symmetry. 

PRODUCTION   OF   PLANE   POLARIZED   LIGHT. 
Plane  polarized  light  may  be  produced  from  common  light: 

*  This  conforms  strictly  to  the  usage  in  the  uniaxial  which  is  a  special  case  of 
biaxial  with  the  angle  between  the  optic  axes  zero,  the  acute  bisectrix  being  in  the 
direction  c- 

t  In  terms  of  principal  indices  these  might  be  written  Positive,  vibration  of  y  =Bxa, 
Negative,  vibration  of  a=Bxa- 


108  CR  YSTALLOGRAPHY. 

1.  By  reflection  from  a  non-metallic  surface.* 

2.  By  double  refraction  and  absorption. f 

3.  By  double  refraction  and  total  reflection. 

NicoPs  Prisms. 

The  third  method  is  most  used  and  while  many  polarizing  prisms 
exist  all  are  based  on  the  prism  described  by  William  Nicolt  in 
1828. 

It  may  be  briefly  described  as  consisting  of  a  cleavage  of  iceland 
spar  (calcite)  with  a  length  about  three  times  its  breadth. 

Let  aBdC,  Fig.  240,  be  a  principal  section  through  the  optic 
axis  XY  and  the  short  diagonals  aB  and  Cd  of  opposite  small 
cleavage  faces. 

To  secure  the  needed  directions  these  small  faces,  at  70°  52' 
and  109°  8'  to  the  edge  BD,  are  ground  away  and  replaced  by 
faces,  indicated  by  AB  and  CD  at  68°  and  112°,  to  the  edge. 
The  prism  is  then  cut  through  by  a  plane  through  AD  at  right 
angles  both  to  the  new  terminal  faces  and  to  the  principal  section. 
The  parts  are  carefully  polished  and  cemented  by  Canada  balsam, 
the  index  of  refraction  of  which  is  about  1 .54. 

The  index  of  refraction  of  the  ordinary  ray  is  1.658,  that  of  the 
extraordinary  ray  varies  with  the  direction  of  transmission  be- 
tween 1.486  and  1.658.  For  instance,  the  ray  transmitted  parallel 
to  DB  has  an  index  1.516. 

The  general  effect  therefore  of  such  a  construction  is  that  any 
incident  ray  IE,  Fig.  240,  on  entering  is  split  into  two  rays.  The 
ordinary  ray,  with  an  index  of  refraction  of  1.658,  if  incident  at 

*  The  reflected  ray  is  perfectly  polarized  only  when  it  is  at  right  angles  to  the 
refracted  ray.  For  this  particular  angle  of  incidence  (tan  i  =  n}.  The  vibrations 
are  at  right  angles  to  the  plane  through  incident  and  reflected  ray.  With  glass  a 
series  of  parallel  plates  are  used  each  plate  increasing  the  proportion  of  polarized 
light. 

The  device  is  inexpensive  but  it  is  difficult  to  obtain  enough  perfectly  polarized 
light  because  of  the  small  angle  to  which  the  incident  rays  must  be  limited. 

t  Double  refraction  and  absorption.  Certain  substances,  such  as  tourmaline, 
absorb  one  ray  much  more  rapidly  than  the  other,  and  a  thickness  can  be  chosen 
for  which  one  ray  is  totally  absorbed,  the  other  being  partially  transmitted  with 
vibrations  all  in  one  plane. 

The  very  simple  polariscope  called  the  tourmaline  pincers  depends  on  this  prin- 
ciple but  the  light  is  colored. 

t  Edinb.  New  Phil.  Jour.,  VI,  83-94. 


CR  YSTALL  O-  OPTICS. 


109 


the  balsam  at  an  angle  greater  than  its  critical  angle,  follows  some 
path  EJ  and  is  totally  reflected  at  the  balsam  along  JH  and 
absorbed  by  the  blackened  walls  about  the  nicol. 

The  extraordinary  ray,  however,  follows  some  path  EF  and  if 
its  index  is  less  than  1 .54,  is  simply  diverted  a  little  by  the  balsam, 
say,  along  FS,  and  thereafter  following  the  path  SG  parallel  EF 
emerges  travelling  parallel  the  incident  ray  IE  but  plane  polarized 
and,  according  to  the  assumption  made  on  describing  double  refraction 


FIG.  240. 


FIG.  241. 


Jo     /. 


in  calcite,  with  its  vibration  direction  in  the  plane  of  AB  the  short 
diagonal  of  the  face  of  the  nicol. 

Fig.  240  shows  the  nicol  section  with  light  incident  in  the 
direction  IE  parallel  the  length  of  the  nicol.  In  Fig.  241  the 
construction  considers  light  incident  at  any  angle  and  shows  that 
only  the  rays  between  J0  and  Ie  will  yield  pure  extraordinary 
rays,  since  these  are  furnished  only  by  light  rays  incident  at 
the  balsam  between  the  critical  angles  of  the  ordinary  and 


HO  CRYSTALLOGRAPHY. 

extraordinary  ray.*  This  so-called  "opening  angle"  of  the  nicol 
is  about  25°. 

The  critical  angle  of  the  ordinary  ray  is  EKV  =  68°  13',  Fig. 
241,  corresponding  to  an  incident  ray  J0  at  37°  59'  to  EZ.  Both 
components  of  any  ray  incident  at  an  angle  greater  than  37°  59' 
would  be  transmitted. 

The  critical  angle  of  the  varying  extraordinary  ray  is  ENW 
=  81°  34',  corresponding  to  an  incident  ray  Ie  at  13°  12'  to  EZ. 
Neither  component  of  any  ray  incident  at  an  angle  less  than 
13°  12'  would  be  transmitted.  That  is,  the  useful  or  opening 
angle  of  the  nicol  is  I0EIe  =  37°  59'  —  13°  12'  =  24°  47'. 

This  opening  angle  may  be  increased  considerably  by  different 
constructions. 

For  instance,  the  Hartnack-Prazmowsky  prism  is  calcite  with 
the  end  faces  at  right  angles  to  the  others  and  with  linseed  oil 
instead  of  balsam.  In  others  the  material  is  different.  Sodium 
nitrate  prisms  have  been  made,  but  while  optically  good  were 
hygroscopic.  Combinations  of  glass  and  calcite  are  successful 
as  polarizers  but  not  as  analyzers  because  they  are  not  achromatic. 
In  some  devices  the  ordinary  ray  is  transmitted  instead  of  the 
extraordinary. 

THE  FUNDAMENTAL   PHENOMENA   BETWEEN   CROSSED    NICOLS. 

Crossed  Nicols. 

The  term  nicol  is  hereafter  used  to  designate  any  form  of 
polarizer.  If  two  nicols  are  placed  so  that  the  light  from  one 
reaches  the  other,  the  light  will  go  through  the  second  unchanged 
if  the  faces  of  the  nicol  are  parallel,  but  if  one  is  rotated  the  light 
emerging  from  the  second  nicol  will  vary  in  intensity  with  their 
relative  position. 

Let  PPr  Fig.  242  be  the  direction  of  vibration  of  light  from 
the  first  nicol  and  CP  its  amplitude,  then  if  A  A'  is  the  direction 
of  vibration  of  the  extraordinary  ray  in  the  second  nicol  and  BBr 
that  of  the  ordinary  ray  the  components  of  CP  in  these  direc- 
tions will  be  Ca  and  Cb,  of  which  the  former  will  be  transmitted, 
the  latter  totally  reflected  at  the  balsam. 

*  For  elaborate  discussion  see  Johannsen's  "Manual  of  Petrographic  Methods," 
pp.  158-175. 


CR  YSTALL  O-  OPTICS. 


Ill 


If  the  rotation  is  clockwise  Ca  will  decrease  and  at  90°  of  rota- 
tion, with  crossed  nicols,  it  will  be  zero,  that  is,  none  of  the  light 
from  the  first  nicol  will  emerge  from  the  second  nicol  and  the  field 
will  be  dark. 

As  the  rotation  is  continued  Ca  will  increase  until  at  180°  it 
again  equals  CP  and  so  on.  The  first  nicol  is  often  called  the 
Polarizer,  the  second  the  Analyzer. 

FIG.  243. 


/ 


/ 


The  fundamental  phenomena  between  crossed  nicols  upon  which 
all  optical  tests  rest  may  be  described  under  the  headings  Depolar- 
ization, Extinction  and  Interference  and  they  may  be  illustrated 
by  any  simple  combination  of  polarizer  and  analyzer  as  tourmaline 
pincers  or  two  nicols  prisms  set  in  a  hole  bored  in  a  block  of  wood 
and  a  slit  crossing  the  hole  at  right  angles  for  the  insertion  of  the 
crystal  plate. 

Depolarization. 

If  a  plate  of  glass  or  a  section  of  an  isometric  crystal  is  placed 
between  crossed  nicols,  the  dark  field  remains  dark.  But  if  a 
section  of  a  doubly  refracting  crystal  is  so  inserted,  the  field  is  in 
general  illuminated  because  any  ray  of  light  from  the  first  nicol 
emerges  from  the  section  as  two  parallel  rays  with  vibrations  at 
right  angles  to  each  other,  each  of  which  would  furnish  a  com- 
ponent in  the  direction  of  vibration  of  the  second  nicol.  In  other 
words,  the  dark  field  would  be  illuminated,  although  the  nicols 
remain  crossed. 
Extinction. 

If  any  doubly  refracting  crystal  section  is  revolved  between  the 
nicols  in  its  own  plane  until  its  vibration  directions  are  parallel 


112 


CR  YSTALLOGRAPHY. 


to  the  vibration  direction  of  the  nicols  the  light  from  the  first 
nicol  will  be  transmitted  without  change  through  the  section  but 
on  reaching  the  second  nicol  will  be  stopped  because  its  vibration 
direction  is  at  right  angles  to  the  vibration  direction  of  the  second 
nicol.  That  is,  the  light,  which  in  general  passes  through  the 
described  combination  of  crossed  nicols  and  crystal  section,  will 
be  shut  out  or  extinguished  every  90°  or  four  times  during  a 
revolution  of  the  section  in  its  own  plane. 

Interference  of  Monochromatic  Polarized  Light  Between  Crossed 
Nicols. 

Two  rays  of  polarized  light  of  the  same  wave-length,  following 
the  same  path  and  with  vibrations  in  the  same  plane  will  combine 

FIG.  244. 


or  "interfere,"  their  vibrations  either  supplementing  or  opposing 
each  other  according  to  the  so-called  phase  difference  of  the 
rays. 

For  instance,  if  the  light  incident  at  the  lower  surface  of  a 
section  of  a  doubly  refracting  plate  shown  in  Fig.  244  is  polarized, 
monochromatic  and  parallel,  interference  will  take  place  between 
crossed  nicols  as  follows: 

The  less  refracted  ray  FD  from  the  incident  ray  EF  and  the 
more  refracted  ray  BD  from  the  parallel  incident  ray  AB  will, 
after  emergence,  follow  the  same  path  DC  (parallel  to  the  incident 
rays)  but  their  vibrations  will  take  place  in  planes  at  right  angles 
to  each  other. 

There  will  in  general  be  a  phase  difference  between  FD  and  BD 
because  they  are  unequal  in  length,  different  in  vibration  direction, 


CR  YSTALL  O-  OPTICS.  1 1 3 

and,  having  encountered  different  structures,  have  been  retarded 
unequally. 

Reaching  the  analyzer  the  vibrations  of  FD  and  BD  will  be 
brought  into  the  same  plane,  each  furnishing  a  component  in  the 
direction  of  the  vibration  plane  of  this  second  nicol,  and  therefore, 
they  will  combine  or  "interfere." 

Similarly  from  each  point  of  the  upper  surfaces  of  the  crystal 
section  there  will  emerge  two  rays  with  the  same  phase  difference 
as  BD  and  FD  which  will  be  brought  by  the  analyzer  to  the  same 
"interference." 

For  the  understanding  of  interference  between  crossed  nicols 
two  important  limit  cases  must  be  considered. 

Denote  the  difference  in  retardation  of  the  two  rays  by  A  and 
the  wave-length  of  light  by  X  then : 

1.  If  A  =  X,  2X,  3X,    •••-,  n\  the  two  components  following  the 
same  path  will  oppose  and  exactly  neutralize  each  other,  the  light 
will  be  stopped  and  darkness  will  result  for  all  positions  of  the  crystal 
section. 

2.  If  A  =  I/2X,  3/2X,  5/2X  (or  any  odd  multiple  of  i/2\),  the 
two  components  following  the  same  path  will  supplement  each  other 
and  the  field  be  most  strongly  illuminated  for  all  positions  of  the 
crystal  section. 

The  proof  for  the  first  statement  is  as  follows:  Let  PP',  Fig.  245,  represent  the 
direction  of  vibration  and  OP  the  intensity  of  the  light  from  the  first  nicol.  Let  RR' 
and  SS'  represent  the  vibration  (or  extinction)  directions  of  the  doubly  refracting 
plate  and  AAf  the  direction  of  vibration  direction  of  the  second  nicol. 

Then  at  the  instant  of  entering  the  plate  OP  is  resolved  into  components  OM 
and  ON.  OP,  OM  and  ON  will  be  the  same*  phase  and  evidently  also  when  one  of 
the  two  has  gained  relatively,  just  a  wave-length  (or  2  or  3,  etc.,  wave-lengths)  their 
phases  will  still  be  alike,  that  is,  the  components  of  OM  and  ON  in  the  vibration 
direction  A  A'  are  OX  and  OY  equal\  and  in  opposite  directions. 

Practical  Confirmation. — A  wedge  of  doubly  refracting  substance, 
for  instance,  a  little  wedge  of  gypsum  made  by  shaving  down  a 
cleavage  with  a  sharp  knife  or  better  by  rubbing  it  down  will 
show,  in  monochromatic  light  under  low  magnification,  dark  bands 
at  regular  intervals,  which  vary  in  distance  apart  with  the  color 
of  the  light  used  and  correspond  to  differences  between  the  emerg- 
ing rays  of  one,  two,  three,  etc.,  wave-lengths. 

*  If  OP  at  end  of  its  vibration  then  so  are  OM  and  ON,  if  in  middle  so  are  they, 
t  Because  they  are  horizontal  projections  of  equal  parallel  lines  OM  and  PN. 
9 


114  CRYSTALLOGRAPHY. 

INTERFERENCE    COLORS   WITH   WHITE    LIGHT. 

The  "retardation"  A  has  a  definite  numerical  value  dependent 
on  thickness,  direction  and  material.  For  a  given  section  it 
differs  only  slightly  for  different  wave-lengths  of  light.  If  there- 
fore white  light,  which  is  composed  of  many  rays  of  different  wave- 
lengths, is  used  as  a  source  of  light,  the  retardation  A  may  be  at 
the  same  time:  (a)  approximately  a  multiple  of  the  wave-length 
of  light  of  one  or  more  colors,  which  would  therefore  be  shut  out; 
(b)  closely  an  odd  multiple  of  the  half  wave-lengths  of  other  colors 
leaving  these  at  nearly  their  full  intensity,  and  (c)  intermediate, 
with  still  other  colors. 

The  resultant  so-called  interference  color  shown  by  the  section 
of  a  doubly  refracting  substance  between  crossed  nicols  would  be 
the  combination  of  what  is  left  of  the  different  monochromatic 
colors. 
The  Interference  Color  Corresponding  to  a  Given  Value  of  A. 

If  A  be  divided  successively  by  the  wave-lengths  of  the  different 
colors  and  the  quotients  considered,  those  colors  will  be  wholly 
or  nearly  shut  out  for  which  the  quotients  are  closely  i,  2,  3,  4, 
etc.,  and  those  colors  will  be  nearest  their  full  values  for  which 
the  quotients  approach  1/2,  3/2,  5/2,  etc.  For  quotients  of  inter- 
mediate values  the  colors  will  be  partially  shut  out. 

If  then  due  allowance  is  made  for  the  relative  intensities  of  the 
spectrum  colors  the  interference  color  will  be  evident. 

Using  five  prominent  colors  only  an  approximate  determination 
may  be  made  either  graphically  or  by  direct  calculation. 

Graphically. — In  Fig.  246  the  construction  is  as  follows: 

The  first  vertical  line  is  the  A  scale  divided  into  spaces  representing  100  /z/z 
(millionths  of  a  millimeter). 

The  remaining  five  vertical  lines  are  divided  respectively  into  spaces  proportionate 
to  the  half  wave-lengths  (in  millionths  of  a  millimeter)  for  Hi  (violet),  393.3;  Fi 
(blue),  486.0;  E  (green),  526.9;  Di  (yellow),  589.5;  C  (red),  656.2;  A  (red)  760.4. 

Taking  any  length  as  indicating  maximum  light  draw  lines  of 
this  length  opposite  I,  2,  3,  4,  wave-lengths.  Draw  parallel  lines 
regularly  diminishing  to  the  length  zero  opposite  1/2,  3/2,  5/2, 
etc.,  wave-lengths. 

The  lines  represent  the  proportion  of  the  violet,  yellow,  etc.,  present.  They  do 
not  show  the  coloring  intensities  which  in  the  order  of  colors  stated  are  roughly 

O,   I,  2,  3,  6,  2. 


CR  YSTALL  O-  OPTICS. 


A  fair  approximation  therefore  to  the  interference  color  corre- 
ponding  to  any  value  of  A  will  result  bv  following  a  horizontal 


I 

/                     1 

?v   i 

F 

7       1 

IG.    246. 

>/       < 

nr 

£ 

f 

£ 

I 

. 

Tron  Gray. 

^^ 

^= 

•=^ 

JEEE 

Pale  Gray. 

I 

£«'    Pure  White. 

' 

®    Pale  Yelloxr. 
£    Bright  Yellcw. 

-     —  *— 

—  i 

__—  _= 

•^zi 

...^^ 

7    Orange  Red. 
Red. 

•^^ 

jn: 

J 

5 

( 

— 

• 

.' 

z::=:: 

"^Z 

1    Blue. 
Jjj   Bluish  Green. 

;  —  - 





— 

o-    Yellowish  Green. 

— 

S,    Yellow. 

— 

- 

- 





Orange  Red. 

^ 

— 

— 

,    "—  — 

-            • 

Red. 
Violet  (sensitive  tint  No.  2). 

- 





• 

— 

-Blue. 
Bluish  Green., 



•  — 



— 

j 

••«'    Green. 

~  

~ 

"= 

— 

o    Yellowish  Green. 
3,    Yellow. 

* 

— 

- 





r<                 .-Rose  Red- 
Reddish  Carmine. 

— 



- 

— 



Purplish  Carmine. 
I    Violet  Gray  (sensitive  tint 

- 



. 

~ 

-= 

(     Bluish  Gray        No-  3>« 



— 



- 



- 

j 

- 

%    Pale  Green. 
1 



J 

— 

o 

a 

—  - 

•• 

'  •  "• 

;• 

r»    White  of  high 
o           order. 

straight  edge  across  from  this  value  and  noting  the  relative  lengths 
of  the  horizontal  lines. 


116  CRYSTALLOGRAPHY. 

By  Calculation. — For  instance  let  A  =  900  MM  (millionth  of  a 
millimeter). 

QOO 

HI — Violet =  2.29  over  1/2  present. 

O  z^O 

FI — Blue       —  =  1.85  about  3/10  present. 
400 

E  — Green  -  -  =  1.70  about  1/2  present. 

527 

QOO 

DI — Yellow =  1.52  almost  all  present. 

59° 

QOO 

C  — Red       —  —  =  1.37  about  3/4  present. 

That  is,  the  color  is  made  up  of  almost  all  the  yellow,  3/4  of  the 
red,  about  1/2  of  the  violet  and  green  and  3/10  of  the  blue. 

Multiplying  by  the  relative  intensities  for  each  color,  as  stated 
in  graphical  method,  the  following  proportions  result:  Violet  o, 
blue  3/10,  green  I,  yellow  6,  red  3/2.  That  is,  yellow  greatly  pre- 
dominates. The  red  more  than  balances  the  green  and  the  blue 
and  the  remaining  red  tints  the  dominant  yellow,  forming  orange. 

The  Interference  Color  Scale. 

The  interference  colors  grade  from  black  for  A  =  o,  to  colors 
not  clearly  distinguishable  from  white  with  A  beyond  2,000  MM- 

Because  the  colors  repeat  to  some  extent  periodically  they  are 
divided  into  so-called  "Orders,"*  the  convenient  transition  color 
between  orders  being  a  so-called  sensitive  violet  because  very 
minute  changes  in  A  result  in  decided  changes  to  blue  or  red. 

Order.  Last  Color.  Value. 

First Sensitive  violet,  No.  i 575  pp. 

Second Sensitive  violet,  No.  2 1,130  IJL/J. 

Third Sensitive  violet,  No.  3  (violet  gray) 1,652  /JL/J, 

In  Fig.  246  the  names  of  the  principal  colors  of  the  color  scale 
are  approximately  opposite  the  corresponding  values  of  A. 

The  first  order  colors  start  with  black  and  pass  through  shades 

*  These  are  not  quite  Newton's  orders,  which  end  respectively  at  A  =  551,  1101, 
and  1652.  This  division  gives  no  sensitive  violet  in  the  first  order,  one  in  the  second, 
and  two  in  the  third. 


CR  YS  TA  LL  O-  OPTICS.  117 

of  gray  to  nearly  pure  white*  at  A  =  250  /zju.  Beyond  this  the 
shorter  waves  are  more  completely  shut  out  and  the  yellow 
orange  and  red  reach  a  maximum. 

The  second  order  colors  are  in  general  bright  spectrum  colors — 
Indigo,  blue,  green,  yellow,  orange,  red. 

The  third  order  colors  are  paler  and  more  complex  because  with 
increasing  values  A  becomes  an  approximately  perfect  multiple 
of  i/2\  for  an  increasing  number  of  wave-lengths.  For  example: 
A  =  1500  is  5/2\  for  orange  red,  7/2\  for  indigo,  3\  for  green,  2\ 
for  red,  4\  for  violet.  The  resultant  total  effect  is  between  car- 
mine and  purple. 

The  higher  orders. — With  the  still  higher  values  for  A  the  pale- 
ness and  indefiniteness  of  the  colors  are  still  more  noticeable  and 
beyond  the  fourth  order  the  colors  are  usually  grouped  as  "  high 
order  whites." 

The  Polarizing  Microscope  and  Its  Adjustment. 

The  modern  polariscope  for  the  study  of  crystals  is  the  polarizing 
microscope.  With  the  proper  attachments  it  yields  all  the  desired 
tests  either  with  relatively  large  or  microscopic  quantities  of 
material. 

The  simplest  polarizing  microscope  necessarily  includes  the 
essentials  of  an  ordinary  microscope  (a  stand  supporting  a  tube 
carrying  objective  and  ocular,  a  platform  or  stage  and  means  of 
focusing  and  illuminating),  and  in  addition  a  nicol,  "the  polar- 
izer," below  the  object,  to  polarize  the  incident  light,  and  another 
above  the  objective,  "the  analyzer"  arranged  to  be  thrown  in  or 
out  and  "  crossed  "  with  respect  to  the  polarizer. 

To  these  essentials  may  be  added  many  devices  and  attachments 
for  special  purposes  resulting  in  a  highly  complex  piece  of  mechan- 
ism. For  general  work  something  between  the  two  extremes  is 
most  satisfactory. 

The  Illuminating  System. 

This  consists  of  the  mirror,  and  the  condensing  lens  and  some- 
times a  diaphragm. 

The  mirror  has  one  plane  face  and  the  other  concave.     It  may 

*  For  this  value  the  diminished  intensities  of  the  colors  are  relatively  nearly  as 
in  white  light. 


Il8  CRYSTALLOGRAPHY. 

be  tipped  in  any  direction  and  usually  has  a  limited  up-and-down 
motion. 

Its  purpose  is  to  reflect  light  from  the  source  to  the  object. 
The  plane  mirror  should  be  used  for  sunlight  or  for  low  magnifica- 
tions, the  concave  for  high  magnifications  without  the  condenser, 
for  very  high  magnifications  and  interference  phenomena  the 
plane  mirror  and  condensing  lens. 

The  condenser  or  condensing  lens  illuminates  the  object  with  a 
cone  of  light.  In  some  instruments  it  rests  on  the  top  of  the 
polarizer,  in  others  it  is  swung  into  position  by  a  lever,  being 
attached  to  the  same  system  it  is  raised  with  the  polarizer  and 
at  its  highest  point  is  practically  level  with  the  upper  surface 
of  the  stage. 

The  principal  use  is  in  obtaining  the  so-called  convergent  light 
effects. 

The  best  effects  are  obtained  when  the  condenser*  is  in  focus; 
this  often  is  at  the  highest  point. 
The  Polarizer  and  Analyzer. 

The  nicols  prism  has  been  described  in  detail,  p.  109.  Two 
polarizing  prisms  called  nicols  are  needed  in  the  polarizing 
microscope.  The  lower,  called  "the  polarizer"  can  be  raised  or 
lowered  by  lever  or  screw  and  swung  or  drawn  aside.  Usually  it 
can  be  adjusted  so  that  its  plane  of  vibration  is  either  parallel  or 
diagonal  to  the  cross  hairs  as  in  Fig.  247. 

The  analyzer  is  usually  a  flat-ended  prism  such  as  the  Glan- 
Thompson  placed  above  the  objective  and  arranged  to  slide  in 
and  out  of  the  microscope  tube.  It  frequently  can  be  rotated 
through  90°,  as  in  Fig.  248,  so  that  the  plane  of  vibration  may  be 
placed  cross  or  parallel  to  that  of  the  polarizer. 

In  certain  microscopes  such  as  Fig.   248  both  nicols  can  be 
rotated  together  instead  of  rotating  the  stage. 
The  Objectives  and  Oculars. 

Different  objectives  and  oculars  are  used  in  crystal  work,  never 
of  very  high  power,  the  most  used  combinations  varying  in 
magnification  from  50  to  400  diameters. 

*  Focus  on  a  section  with  a  low  power  objective,  turn  plane  mirror  until  some 
object,  tree,  window  bar,  etc.,  is  in  field.  Raise  and  lower  condenser  until  this 
image  is  sharp,  then  slightly  rotate  mirror. 


CR  YSTALL  O-  OPTICS. 


119 


The  objective  receives  the  light  from  the  object,  focuses  it  and 
produces  a  real  image.  Its  magnifying  power  increases  with  the 
tube  length  of  the  microscope  and  its  resolving  power  or  power 
to  make  details  visible  increases  with  the  number  of  rays  coming 

FIG.  247. 


Leitz  Microscope  No.  30. 

from  the  object  and  on  its  relative  freedom  from  spherical*  and 
chromaticf  aberration. 

*  Unequal  magnification  in  different  parts  of  the  field  and  haziness  due  to  different 
focal  lengths. 

t  Different  focal  lengths  of  light  of  different  colors. 


120 


CR  YSTALL  OGRAPHY. 


FIG.  248. 


Fuess  Microscope  No.  VI. 

Objectives  are  usually  numbered  and  sometimes  marked  in 
terms  of  the  focal  length  ranging  from  low  powers  of  3  inch  to 
high  powers  of  1/12  inch  or  less. 


CR  YSTALL  O-  OPTICS.  1 2 1 

\ 
Oculars. — The  ocular  or  eye  piece  most  used  is  the  Huyghens* 

ocular  made  of  two  plano-convex  lenses  with  their  plane  surfaces 
towards  the  eye,  the  lower  or  field  lens  collects  the  rays  and  lessens 
the  spherical  and  chromatic  aberration.  The  upper  or  eye  lens 
connects  the  rays  into  parallel  rays  and  gives  an  enlarged  inverted 
image  of  the  object.  "Cross  hairs"  or  micrometers  are  placed 
at  the  focal  plane  of  the  field  lens.  The  cross  hairs  usually 
intersect  in  the  line  of  sight  at  right  angles  and  parallel  to  the 
vibration  plane  of  the  nicols. 

To  obtain  high  magnification  it  is  generally  better  to  use  a 
high  power  objective  and  low  or  medium  power  eye  piece  as  the 
higher  power  oculars  cause  indistinctness. 

The  Field  of  View  with  Huyghen's  ocular  is  roughly  in  fractions 
of  an  inch  five  times  the  reciprocal  of  the  magnifying  power  in 
diameters,  e.  g.,  50  diameters  of  the  field  is  i/io  inch. 

The  Path  of  the  Light  and  Formation  of  the  Image. 

The  object  Oi,  Fig.  249,  receives  rays  from  a  mirror,  these  pass 
through  the  diaphragm  CD  and  condenser  system,  then  through 
the  objective  and  cross  at  FI  and  enter  the  lower  or  field  lens  of 
the  eye  piece  giving  a  real\  inverted  image  at  02,  which  is  enlarged 
by  the  upper  or  eye  lens  to  the  virtual  and  still  inverted  image 
at  04. 

The  optical  tube  length  of  the  microscope  is  A,  Fig.  249,  the 
distance  between  the  two  foci  FI  of  the  objective  and  F%  of  the 
eye  lens.  The  magnifying  power  of  an  objective  increases  with 
the  tube  length.  L  is  the  mechanical  tube  length  usually  160 
mm.  and  EP  the  eye  point. 

The  Mechanical  Parts  of  a  Polarizing  Microscope. 

The  Stand. — The  support  to  which  the  other  parts  are  attached. 
Usually  with  a  heavy  horse-shoe  base. 

The  Stage. — The  simple  stage  is  a  circular  disc,  Fig.  247,  with 
a  central  hole.  It  can  be  rotated  about  an  axis  coincident  with 

*  In  the  Ramsden  ocular  the  convex  sides  of  the  two  lenses  face  each  other  and 
the  image  is  not  inverted. 

t  The  real  image  results  when  the  object  is  further  from  the  lens  than  the  focal 
length.  It  is  on  the  opposite  side  of  the  lens  and  can  be  projected.  The  virtual 
image  results  when  the  object  is  nearer  the  lens  than  the  focal  length.  It  can  not 
be  projected. 


122 


CR  YSTALLOGRAPHY. 


the  line  of  sight.  In  some  instruments  it  is  permanently  centered, 
in  some  adjustable.  It  should  be  graduated  so  that  angular 
rotations  can  be  read  to  fractions  of  a  degree.  In  more  elaborate 
instruments  it  has  sliding  screws  ss'  Fig.  248,  and  other  acces- 
sories. 

FIG.  249. 


After  Bausch  and  Lomb. 

Body  Tube  and  Draw  Tube. 

These  carry  most  of  the  optical  parts,  the  draw  tube  sliding  in 
the  body  tube.  In  both  247  and  248  the  draw  tube  is  graduated 
to  show  the  "optical  tube  length,"  A. 

Coarse  and  Fine  Adjustment. 

The  coarse  adjustment  is  usually  a  rack  and  pinion  motion  of  the 
drawing  tube  with  respect  to  the  stand  while  the  fine  adjustment 


CRYSTALLO-OPTICS.  123 

is  by  a  micrometer  screw  with  a  graduated  milled  head,  n,  Fig. 
248,  the  value  of  one  division  usually  being  .01  mm. 

Centering  Screws. 

Two  screws  producing  motion  at  right  angles  and  attached 
either  to  the  objective  holder,  as  in  Fig.  247,  or  to  the  stage. 

Objective  Holder. 

This  is  usually  a  clutch  or  clasp,  k,  Fig.  248,  which  is  really  a 
pair  of  steel  tongs  which  grips  a  collar  on  the  objective  between 
its  jaws.  It  is  always  advisable  to  give  the  objective  a  slight 
twist  after  inserting  it. 

Slots  for  Accessories. 

A  slot  is  always  provided  just  above  the  objective  for  the  inser- 
tion of  the  so-called  test  plates  (quarter  undulation  mica  plate, 
gypsum  red  of  first  order,  quartz  wedge,  etc.).  The  better 
instruments  have  a  second  slot  in  the  telescope  above  the  analyzer 
for  the  introduction  of  a  Bertrand  lens,  /,  Fig.  248,  by  which  the 
interference  figures  are  made  visible. 

ADJUSTMENTS    OF   THE    MICROSCOPE. 

The  resolving  power,  definition  and  freedom  from  much  aberra- 
tion are  judged  by  means  of  selected  slides,  such  as  those  of 
diatoms,  using  a  weak  ocular  and  the  light  from  a  white,  thinly 
clouded  sky. 

Focusing. 

This  should  be  tried  first  with  a  medium  power  objective,  the 
focal  length  of  which  may  be  1/4  inch  or  more.  Set  the  objective 
lower  than  this  and  focus  upward.  In  using  a  high  power  "place 
the  eye  on  a  level  with  the  stage"  and  looking  toward  a  window 
lower  the  objective  until  only  a  thin  film  of  light  remains  between 
the  cover  glass  and  the  lens  and  then  focus  upward.  When  prac- 
ticable, use  a  low  power  as  a  finder. 

Centering. 

Focus  on  a  minute  grain  and  move  the  glass  until  the  grain 
coincides  with  A,  Fig.  250,  the  intersection  of  the  cross  hairs. 
Revolve  the  stage  360°  and  note  the  orbit  of  the  grain.  The  center 
(C)  of  the  orbit  is  the  center  of  rotation.  When  the  grain  is  at  B, 


124 


CR  YSTALLOGRAPHY. 


that  is,  after  180°  rotation,  move  it  half-way  to  A  by  the  two 
FIG.  250.  adjustment  screws  and  the  other  half  by 


moving   the   object  glass, 
operation. 


Repeat  the 


Determining    Vibration     Direction     of 
Lower  Nicol. 

In  the  original  nicols  prism  the  vibra- 
tion direction  is  that  of  the  short  diag- 
onal. In  other  forms  this  direction  needs 
to  be  determined  because  known  dis- 
tinctions can  then  be  made  between 
the  indices  of  refraction,  the  absorption  directions,  etc.  With 
the  upper  nicol  out  rotate  a  section  of  biotite  showing  the  cleavage 
cracks  until  the  position  of  maximum  darkness  is  reached.  The 
plane  of  vibration  of  the  lower  nicol  will  then  be  parallel  to  the 
cleavage  cracks. 

Or  use  a  thin  dark-colored  tourmaline  which  is  darkest  when  the 
vibration  plane  of  the  nicol  is  perpendicular  to  its  optic  or  cf  axis. 
Or,  removing  the  polarizer,  view  the  light  reflected  from  a  plane 
polished  surface  the  surface  will  appear  darkest  when  the  vibration 
plane  of  the  nicol  is  perpendicular  to  it. 

Determining  Magnification. 

The  magnifying  power  of  any  combination  of  lenses  is  the  pro- 
duct of  the  magnifying  power  of  the  objective  and  eye  piece  used. 
A  table  giving  the  magnification  for  each  combination  should 
accompany  each  microscope. 

It  is  usually  stated  in  diameters  and  can  be  obtained  approxi- 
mately by  placing  on  the  stage  a  cover  glass  with  lines  ruled  a 
known  distance  apart,  focusing  on  this  and  obtaining  its  image 
on  a  ground  glass  10  inches  above  the  eye-point.  Then  the 
magnification  in  diameters  is  equal  to  the  distance  apart  of  two 
lines  of  the  image  divided  by  the  distance  apart  of  the  same  two 
lines  on  the  cover  glass.  If  an  Abbe  drawing  apparatus  is  avail- 
able the  lines  may  be  projected  by  this  and  sketched  and  their 
distance  apart  measured. 

Using  a  Microscope. 

The  student  should  sit  upright  with  the  microscope  directly 


CR  YSTALL  O-  OPTICS.  1 25 

in  front  and  both  hands  free  for  manipulation.  Either  eye  may 
be  used,  the  other  being  kept  open.  A  glare  should  be  avoided  and 
that  amount  of  light  used  which  shows  the  structure. 

Dust  should  be  removed  from  lenses  and  nicols  by  a  soft  brush 
or  by  blowing  and  wiping  with  clean  lens  paper.  Sudden  changes 
of  temperature  and  direct  sunlight  are  to  be  avoided.  Lubricate 
only  with  clock  oil.  Cleanse  working  parts  if  necessary  with 
benzene. 

One  of  the  most  satisfactory  polarizing  microscopes  is  the 
Leitz*  No.  30,  sometimes  known  as  the  Berkey  Model  No.  I, 
shown  in  Fig.  247. 

The  adjustable  polarizer  and  analyzer  are  Glan-Thompson 
prisms  and  the  condensing  lens  is  inserted  or  thrown  aside  by 
rotating  the  milled  head  beneath  the  stage. 

The  stage  is  permanently  centered.  The  graduation  can  be  read 
to  i/io  of  a  degree.  The  upper  plate  is  traversed  by  lines  of 
orientation. 

The  graduated  drawing  tube  has  an  inside  diameter  of  24  mm. 

The  Bertrand  lens  is  of  6  mm.  diameter,  can  be  centered  to  the 
microscope,  also  focused  with  the  draw-tube. 

The  Fuess  microscope, f  Model  VI,  Fig.  248,  is  planned  to  fit 
a  large  number  of  accessory  devices  and  is  especially  characterized 
by  the  arrangement  for  simultaneous  rotation  of  polarizer  and 
cap  analyzer,  by  the  cogs  rZ,  r'  Z' ,  the  object  remaining  at  rest, 
but  the  same  relative  change  taking  place  as  if  the  stage  were 
revolyed  and  the  nicols  at  rest. 

There  is  an  elaborate  mechanical  stage,  the  rotation  of  which 
can  be  read  to  minutes  and  has  quick  rotation  by  hand,  slow  rota- 
tion by  ratchet,  and  sliding  motions  in  two  directions. 

Preparation  of  Material  for  Optical  Testing. 

As  most  observations  are  made  by  transmitted  light  it  is  neces- 
sary to  prepare  the  objects  so  that  they  will  transmit  light  and 
not  overlap. 

Sections  in  Crystallographic  Directions. 

The  tests  unless  otherwise  specified  require  what  is  known  as 
''plane  parallel"  plates,  that  is,  that  the  light  shall  enter  and 

*  E.  Leitz,  Wetzlar,  Germany,  and  N.  Y. 
t  R.  FueSvS,  Steglitz,  Germany. 


126  CRYSTALLOGRAPHY. 

emerge  from  essentially  parallel  surfaces.  Such  parallel  surfaces 
may  be  opposite  faces  of  a  crystal  or  cleavage,  or  a  face  may  be 
cemented  to  glass  and  an  opposite  artificial  face  ground  on  or  a 
section  not  parallel  to  any  known  face  may  be  made  at  any  angle 
and  ground,  and  verified  goniometrically  with  reference  to  other 
faces. 

Rock  Sections. 

A  fragment  may  be  chipped  from  the  mass  or  a  thin  slice  cut 
from  it  with  an  endless  wire  fed  with  carborundum  or  by  a  circular 
metal  disc  charged  with  diamond  dust.  One  side  is  ground 
smooth  and  polished  and  cemented  to  glass  and  this  ground  down 
usually  to  a  thickness  of  .03  to  .04  mm.  on  a  rotating  disc  fed 
with  carborundum  or  emery. 

After  cleaning  the  thin  fragment  is  cemented  to  glass  by  Canada 
balsam,  and  covered  with  a  cover  glass  of  .10  to  .15  mm.  thickness, 
using  the  same  cement. 

Good  sections  require*  very  careful  lapidary  work  and  satis- 
factory tools  and  are  to  a  great  extent  made  by  skilled  workmen. 
Crushed  Fragments. 

In  mineral  testing  much  more  rapid  work  can  be  done  with  the 
so-called  "crushed  fragment"  sized  by  screens  to  an  average 
thickness  of  .03  to  .04  mm.  The  method  of  preparing  suggested 
is  as  follows: 

A  small  fragment  is  crushed  by  pressure  in  a  small  agate  mortar 
(or  by  pounding  on  a  steel  plate  with  a  hammer).  Grinding  is 
avoided.  The  crushed  material  is  then  sieved  through  a  small 
loo-mesh  screen  f  upon  a  I2o-mesh  screen,  the  finer  portion  pene- 
trating that.  The  particles  remaining  on  the  i2O-mesh  screen  are 
'shaken  out  on  a  clean  paper  and  a  few  fragments  are  placed  on 
an  object  glass  by  a  flattened  wire  or  knife  point.  A  drop  of  a 
monobromnaphthalin  or  other  liquid  is  placed  to  one  side  and  the 
powder  is  drawn  into  it  by  a  tilted  cover  slip  which  is  then  placed 
in  position. 

*  The  process  of  preparation  is  described  in  detail  in  Chapter  V  of  Luquer's 
"Minerals  in  Rock  Sections,"  and  in  pp.  190-195,  Iddings'  "Rock  Minerals"  and 
other  similar  works. 

f  Easily  made  by  boring  a  one  inch  hole  through  two  square  pieces  of  soft  wood, 
say  2  in.  x  2  in.  x  ^  in.,  inserting  the  wire  gauze  between  and  driving  a  pin-like  brad 
near  each  corner. 


CR  YSTALLO-OPTICS.  127 

a  monobromnaphthalin  has  an  index  of  refraction  of  about 
1.655.  It  forms  a  plane  parallel  sheet  between  the  object  glass 
and  cover  glass,  and  eliminates  the  effects  due  to  irregular  surfaces 
of  the  enclosed  particles  more  or  less  perfectly  as  its  indices 
approximate  or  differ  from  those  of  the  liquid. 

THE  OPTICAL  TESTS  WITH  THE  POLARIZING 
MICROSCOPE. 

Determining   Isotropic    or    Anisotropic.     (Singly    refracting    vs. 
Doubly  refracting.)     (See  Depolarization,  p.  in.) 
With  crossed  nicols  and  (usually)  white  light  and  the  condensing 
lens   removed  or  lowered.     Using  moderate  power,   focus  with 
upper  nicol  out,  then  push  in  the  nicol  and  rotate  the  stage. 

Isotropic. 

If  the  field  is  dark  throughout  rotation  the  substance  is  singly 
refractive  in  this  direction.  If  powder  is  being  used  the  grain 
may  be  made  to  turn  in  the  liquid  by  pressure  with  a  point  on  the 
cover  glass  and  other  directions  tried  or  a  convergent  light  test 
may  be  made. 

Anisotropic. 

The  field  is  dark  at  intervals  of  90°  and  elsewhere  illuminated, 
and  often  colored. 

It  is  to  be  noted  that  "local"  double  refraction,  varying  in 
different  places,  may  occur  as  a  result  of  strain  in  singly  refracting 
substances. 

DETERMINING   INDICES    OF   REFRACTION. 

While  the  methods  of  determining  indices  of  refraction,  p.  97, 
are  essentially  the  same  for  all  substances,  it  is  only  optically 
isotropic  substances,  p.  99,  such  as  liquids,  glasses  and  isometric 
crystals  which  with  monochromatic  light  and  constant  tempera- 
ture have  each  one  index  of  refraction  whatever  direction  of  trans- 
mission is  used. 

In  any  doubly  refracting  substance  the  refractive  indices  vary 
with  the  direction  of  vibration  of  the  light  rays  and  if  the  problem 
is  determining  the  principal  indices  of  refraction  certain  definite 
directions  of  transmission  must  be  secured.  When  this  is  not 
done  the  indices  obtained  are  only  intermediate  indices. 

Uniaxial   crystals,   p.    102,   although   singly   refracting  in  one 


128  CRYSTALLOGRAPHY. 

direction,  give  two  indices  of  refraction  for  any  other  direction  of 
transmission;  one  of  these  is  constant  whatever  the  direction, 
the  other  varies  between  limits,  the  limiting  values  being  the 
principal  indices.  Biaxial  crystals,  p.  105,  have  two  directions 
of  single  refraction  and  two  indices  for  each  other  direction  of 
transmission  and  there  is  no  constant  index. 

METHODS    WITH   LIQUIDS    OF   KNOWN   INDICES. 

In  these  methods  involving  a  comparison  with  the  known 
indices  of  liquids,  a  series  of  liquids  which  are  transparent,  stable 
and  without  action  on  instrument  or  substance  are  required.  The 
number  needed  will  depend  upon  the  purpose,  whether  simply  to 
classify  in  groups  or  to  obtain  as  closely  as  possible  the  true 
indices. 

Simple  liquids  or  mixtures  may  be  used.  Johannsen  gives 
a  list  of  about  seventy,  ranging  from  water,  1.33,  to  molten- 
selenium,*  2.92. 

Van  der  Kolkf  particularly  recommends  about  fifty,  ranging 
from  1.33  to  1.93,  and  Wright, %  from  mixtures  of  a  comparatively 
small  number  of  liquids  obtains  any  desired  value  between  1.45 
and  1.96. 

The  liquids  should  be  kept  in  small  stoppered  and  capped 
bottles,  preferably  blackened  and  in  systematic  order.  The  deter- 
mination of  the  index  of  any  liquid  at  ordinary  room  temperature 
may  be  made  quickly  with  a  simple  total  refractometer,  p.  133. 
If  a  piece  of  ground  glass  is  placed  on  the  drop  of  liquid  the  limit 
line  of  the  liquid  alone  appears. 

Determining  the  Index  of  Refraction  by  the  Becke  Line. 

This  test  is  based  upon  the  occurrence  of  total  reflection  at  a 
vertical  boundary  between  two  substances  of  different  indices 
and  a  consequent  concentration  of  light  on  the  side  of  the  substance 
with  the  higher  index  (denser  substance). 

In  Fig.  251  let  BL  be  the  vertical  boundary  between  the  denser 

*  "Manual  of  Petrogra] >hic  Methods,"  p.  260. 

t"Tabellen  zur  mikroskopischen  Bestimmung  der  Mineralien,"  von  J.  L.  C. 
Schroeder  van  der  Kolk,  2d  ed.,  Wiesbaden,  1906. 

t  "  Methods  ot  Petrographic  Microscopic  Research,"  F.  E  Wright,  Carnegie  Inst., 
1911,  p  98.  See  also  Menvin,  Jour  Wash.  Acad.  Set.,  3,  35. 


CR  YSTALL  O-  OPTICS. 


129 


FIG.  251. 


(shaded)  and  less  dense  substances  and  let  the  microscope  be 
focused  at  O.  Then  as  explained,  p.  98,  all  the  oblique  rays  in 
the  less  dense  medium  incident  at  the 
contact  plane  will  pass  into  the  more 
dense,  for  instance,  AO  will  continue 
as  Oa,  whereas  of  the  rays  in  the 
denser  medium  all  incident  at  the 
contact  plane  at  more  than  the  crit- 
ical angle  NOT  will  be  totally  re- 
flected, for  instance,  CO  will  continue 
as  Oc,  and  only  the  remaining  rays 
pass  into  the  less  dense  medium. 

Evidently,  therefore,  if  the  light  is  narrowed  by  a  light  stop  or 
iris  or  by  lowering  the  polarizer,  there  will  be  a  strong  concentra- 
tion of  the  light  on  the  side  of  the  denser  medium. 

On  slightly  raising  the  objective  the  focal  plane,  for  instance 
PP,  cuts  the  series  of  concentrated  rays  in  a  broadening  band 
giving  the  effect  of  a  bright  band  moving  into  the  denser  substance. 

This  test  is  made  with  a  high  power  objective  and  a  light  stop 
below  the  stage  upon  a  fragment  or  grain  with  an  approximately 
vertical  boundary  or  edge  and  surrounded  by  a  liquid  of  known 
index. 

If  singly  refracting  any  position  of  the  fragment  will  give  the 
same  result,  if  doubly  refracting  the  positions  of  extinction  will 
give  the  greatest  and  least  values. 

With  both  nicols  in,  the  stage  is  revolved  until  the  grain  is 
black.  The  upper  nicol  is  then  drawn  out,  the  condensing  lens 
and  lower  nicol  lowered  or  a  light  stop  used  to  prevent  the  entrance 
of  divergent  rays,  and  the  microscope  sharply  focused  on  the 
vertical  boundary.  If  the  objective  is  now  raised  slightly,  a  line 
of  light,  parallel  to  the  boundary,  will  appear  to  move  into  the 
substance  which  has  the  higher  index.  By  lowering  the  objective 
the  white  line  is  moved  in  the  opposite  direction. 

The  method  will  detect  differences  of  .001,  therefore  with  a 
sufficient  number  of  liquids  will  determine  the  true  indices  to  this 
degree  of  accuracy. 
Indices  of  Refraction  by  Oblique  Illumination. 

Van  der  Kolk   Test. — If  any  fragment  with  tapering  edges  is 
immersed  in  a  liquid  it  will  act  like  a  lens,  and  either  concentrate 
10 


130 


CR  YSTALLOGRAPHY. 


or  disperse  the  light  as  the  surrounding  liquid  is  of  lower  or  higher 
index. 

When  viewed  with  ordinary  central  illumination  the  effect  in 
either  case  is  a  dark  border,  indicating  merely  a  difference  in 

indices. 

FIG.  252.  FIG.  253. 

"7 


If,  however,  by  tipping  the  mirror,  or,  better,  using  the  con- 
denser and  interposing  a  card  or  other  obstruction  to  the  light 
rays  on  one  side  the  illumination  is  made  inclined,  different  effects 
will  be  obtained,  as  shown,  Fig.  252,  in  which  the  fragment  F 
is  the  denser  and  the  bright  side  is  towards  the  card  C  and  Fig. 
253,  in  which  the  liquid  L  has  the  higher  index  and  the  bright  side 
of  the  fragment  F  is  away  from  the  card  C.  0  is  the  objective. 

To  obtain  the  results*  stated  hereafter  this  test  requires  a 
medium  power  objective  and  condensing  lens. 

With  both  nicols  in,  revolve  the  stage  until  the  grain  is  dark. 
Then,  with  the  upper  nicol  out  and  the  grain  in  focus,  slide  a 
sharp-edged  card  below  the  lower  nicol,  drop  the  condenser  until 
the  edge  of  the  card  is  sharply  focused,  then  drop  a  little  further. 
Move  the  card  slowly  toward  the  grain  and  notice  which  side  of 
the  grain  becomes  the  brighter. 

Bright  side  of  grain  toward  card — Index  grain  greater  than 
index  liquid. 

Bright  side  of  grain  away  from  card — Index  grain  less  than  index 
liquid. 

If  the  index  of  the  grain  is  just  that  of  the  liquid  for  yellow 

*As  explained  by  Wright,  Am.  Jour.  Sci.,  21,  362,  1906,  these  phenomena  can 
be  reversed  by  raising  or  lowering  the  condenser.  For  the  position  of  the  card  chosen 
(below  the  focus  of  the  condenser)  the  results  appear  as  stated  below. 


CRYSTALLO-OPTICS.  131 

light,  the  grain  will  be  bordered  by  red  on  the  side  near  the  card 
and  blue  on  the  opposite  side. 

METHODS   AVAILABLE   WITH    GREATER   THICKNESSES. 

Due  de  Chaulnes  Method. 

This  method  depends  on  the  fact  that  if  an  image  0,  Fig.  254, 
is  accurately  focused  and  then  a  transparent  plane  parallel  plate 
interposed  between  it  and  the  objective 
the  image  is  blurred  and  only  becomes 
clear  again  when  the  objective  is  raised 
a  distance  00'.     The  rays  OA  and  OB 
are  refracted  on  emergence  and  0  ap- 
pears to  be  at  O'. 

It  may  be  shown*  that  the  displace- 
ment 00'  or  Ms  a  function  of  the  thick- 
ness T  and  the  index  of  refraction  of 
the  substance. 

The  particular  applicability  of  the  method  is  for  cut  stones 
and  crystals  of  high  indices.  It  requires  opposite  parallel  faces.f 
The  manipulation  is  as  follows:  Set  the  fine  adjustment  screw  of 
the  microscope  near  the  upper  part  of  its  motion,  and  place  a 
minute  spot  of  ink  on  the  object  glass.  Center  this  spot,  cover 
it  with  the  crystal  plate  and  focus  upon  the  ink  spot  through  the 
plate  as  sharply  as  possible.  Remove  the  plate  without  disturb- 
ing the  object  glass;  then,  using  the  fine  adjustment  only,  and 
keeping  count  of  the  number  of  rotations,  lower  the  objective 
until  the  spot  of  ink  is  again  in  focus.  Measure  the  thickness 
of  the  plate  with  a  micrometer  gauge  and  denote  this  thickness 
by  r,  and  the  displacement  or  change  in  focal  length  by  t. 


n  = 


T-  t' 
Simple  Refractometers. 

Refractometers  based  upon  the  principle  of  total  reflection,  in 
which  the  indices  of  refraction  can  be  rapidly  determined  upon 
polished  or  natural  surfaces  from  a  millimeter  in  diameter  up  are 

*  If  one  good  face  exists  a  second  parallel  may  be  imitated  by  a  drop  of  liquid 
and  a  bit  of  cover  glass. 

t  Iddings,  "Rock  Minerals,"  p.  120. 


1 32  CR  YSTALLOGRAPHY. 

now  considerably  used  in  testing  gems  and  could  well  be  used 
more  in  determining  minerals. 

The  surface  of  contact  is  the  diametral  plane  of  a  glass  hemi- 
sphere of  very  high  index  of  refraction. 

There  are  two  methods  of  admitting  the  diffused  incident 
light: 

1.  From  above  the  plane  of  contact.     The  method   of  grazing 
incidence,  Fig.  255,  all  incident  rays  bent  towards  the  normal,  the 
last  ray  iO  to  enter  being  that  parallel  to  the  contact  plane,  which 
emerges  along  Or,  hence  the  field  of  a  telescope  in  the  direction  rO 
would  only  have  its  lower  half  illuminated  or  allowing  for  the  lens 
it  would  appear  as  shown. 

2.  From  below  the  plane  of  contact.     The  method  of  total  reflec- 
tion proper,  Fig.  256,  all  rays  incident  at  more  than  the  critical 

FIG.  255.  FIG.  256. 


angle  Noi  are  totally  reflected  while  those  incident  at  smaller 
angles  are  largely  transmitted  through  the  crystal.  The  field  of 
a  telescope  in  the  direction  rO  therefore  receives  more  light  in  the 
upper  half  than  in  the  lower  and,  allowing  for  the  lens,  it  appears 
as  shown. 

Obviously  light  admitted  both  above  and  below  produce  counter- 
acting effects. 

The  manipulation  is  as  follows: 

Place  a  drop  of  liquid  of  known  index  of  refraction  on  the  center 
of  the  glass  of  the  instrument;  on  this  place  the  crystal  face. 
Admit  light  from  below  or  from  above  but  not  both,  as  counter- 
acting effects  are  obtained,  and  use  the  sodium  flame.  If  only  the 
limit  line  for  the  liquid  is  found,  repeat  with  a  liquid  of  higher 
index  of  refraction. 

Carefully  revolve  the  crystal,  keeping  the  same  face  in  contact 
with  the  glass.  If  the  revolution  produces  no  movement  in  the 


CR  YSTALL  O-  OPTICS. 


133 


FIG.  257. 


limit  line  or  lines,  the  value  is  read  and  the  note  made  that  the 
substance  is  probably  either  amorphous  or  isometric.  If  the  rev- 
olution produces  obvious  movement,  and  two  lines  are  obtained, 
both  are  read  when  at  their 
greatest  distance  apart.  It 
should  be  noted  whether  one 
(uniaxial)  or  both  lines  (bi- 
axial) move  during  the  revo- 
lution. 

In  the  simpler  instruments 
such  as  the  Fuess  Simple 
Refractometer  Model  4, 
shown  in  Fig.  257,  in  section, 
1/2  scale,  or  the  Herbert 
Smith  refractometer  shown 
in  outline;  full  scale,  in  Fig.  258,  the  resulting  sharply  divided 
light  and  shade  are  viewed  through  the  eye  piece  on  a  scale  5, 
Fig.  257. 

FIG.  258. 


The  glass  of  the  hemisphere  in  both  instruments  has  an  index 
of  refraction  a  little  over  1.8.  The  scales  read  to  1.8.  Fig.  259 
shows  the  appearance  of  the  scale  with  a  singly  refracting  sub- 
stance of  index  1.49,  Fig.  260  shows  the  scale  with  a  doubly  refract- 
ing substance  with  indices  I  66  and  1.70. 


134 


CR  YSTALLOGRAPHY. 
FIG.  259.  FIG.  260. 


Determining  the  Sign  of  Elongation. 

The  direction  in  which  a  crystal  or  a  crystal  section  is  longest 
is  called  its  elongation  (or  sometimes  its  principal  zone).  This 
direction  in  uniaxial  crystals  is  often  the  direction  of  the  axis  c 
and  in  the  needles,  fibers,  etc.,  obtained  by  crushing  it  is  connected 
with  the  structure,  especially  the  cleavage. 

If  the  elongation  is  parallel  or  approximately  parallel  to  one 
of  the  vibration  (extinction)  directions  of  the  fragment  or  section 
a  useful  subdivision  results  by  determining  whether  this  vibration 
direction  corresponds  to  the  faster  or  to  the  slower  ray. 

The  vibration  (extinction)  directions  in  the  section  are  found 
and  the  stage  is  revolved  45°  from  that  extinction  position  which 
is  nearest  the  "elongation"  and  the  interference  color  is  noted. 

A  test  plate  of  known  retardation  A  and  on  which  the  directions* 
of  vibration  X  and  Z  (or  a  and  c)  of  its  fastest  and  slowest  rays 
are  marked  is  then  inserted  in  the  slot  above  the  ocular.  The 
changes  in  color  and  the  moving  in  or  out  of  the  color  bands  along 
the  periphery  of  the  section  or  fragments  are  noted. 

If  the  new  color  on  comparison  with  the  color  chart  is  higher 
by  A  of  the  test  plate  and  the  color  bands  move  out,  then  corre- 
sponding vibration  directions  of  substance  and  the  test  plate  are 
parallel  if,  on  the  contrary,  the  new  color  is  lower  by  A  and  the 
color  bands  move  in  the  corresponding  vibration  directions  are 
crossed. 

*  Strictly  X  and  Z  are  the  principal  vibration  directions  of  the  crystal. 


CR  YSTALL  O-  OPTICS.  1 35 

The  directions  of  X  and  Z  therefore  being  now  known  the  follow- 
ing convention  exists. 

The  sign  of  elongation  is  plus  (+)  when  the  elongation  is 
parallel  Z,  and  minus  ( — )  when  the  elongation  is  parallel  X. 

The  test  plate  most  used  is  the  Quarter  Undulation  Mica 
Plate,  a  sheet  of  mica  of  thickness  corresponding  to  a  blue 
gray  interference  color  or  say  140  MM  which  is  i/4\  for  a  medium 
inter-yellow. 

A  very  gradual  tapering  wedge  is  even  better  as  the  succession 
of  colors  prevents  mistake. 

The  slot  above  the  objective  may  be  parallel  to  a  cross  hair 
in  which  case  the  vibration  directions  of  the  test  plate  must  be 
diagonal,  or  the  slot  may  be  diagonally  placed  and  the  test  plate 
made  with  its  length  parallel  X  or  F. 

The  former  method  is  more  convenient  as  the  simple  turning 
of  the  test  plate  upside  down  reverses  its  relation  to  the  crystal 
under  examination. 

DETERMINING   BIREFRINGENCE. 

The  birefringence  or  strength  of  double  refraction  of  any  doubly 
refracting  substance  is  the  difference  between  its  maximum  and 
minimum  indices  of  refraction.  If  these  indices  can  be  deter- 
mined to  the  third  decimal  their  difference  may  be  taken  as  the 
birefringence. 

In  practice  the  birefringence  is  usually  determined  from  the 
retardation  and  consequent  interference  color  and  the  thickness 
of  the  section.  This  gives  the  true  birefringence  of  the  substance 
only  in  exceptional  cases.* 

The  relation  between  retardation  A,  thickness  t  and  refractive 
indices  n\  and  n  for  any  section  are : 

A  =  t(ni  -  n). 

The  retardation  and  the  thickness  must  of  course  be  expressed 
in  the  same  unit. 

The  retardation  can  be  measured  with  considerable  accuracy 
by  compensators.  The  thickness  determination  is  less  accurate. 

*  In  uniaxial  crystals  only  when  the  section  is  parallel  the  optic  axis  and  in  biaxial 
crystals  only  when  the  section  is  parallel  to  the  plane  of  the  optic  axis. 


1 36  CR  YSTALL  OGRAPHY. 

Determining  the  Retardation  by  a  Compensating  Wedge. 

The  process  is  closely  that  for  determining  the  sign  of  elongation. 

The  section  or  grain  is  focused,  the  upper  nicol  pushed  in,  an 
extinction  position  is  found,  and  the  stage  revolved  45°  to  the 
position  of  brightest  illumination.  The  interference  color  is  care- 
fully observed  and  then  a  wedge  of  some  mineral  is  inserted  in  the 
slot  above  the  objective  and  the  interference  color  of  the  combina- 
tion noticed,  if  this  is  higher  than  before  the  conditions  are  reversed 
so  that  the  corresponding  vibration  directions  are  crossed  and  the 
wedge  gradually  pushed  in  until  the  interference  color  is  run  down 
to  black.* 

The  value  of  A  for  the  thickness  of  wedge  interposed  is  the 
desired  value  and  this  may  be  approximated  by  counting  the 
number  of  times  during  the  insertion  of  the  wedge  the  original 
color  reappears,  if  n  times,  then  the  color  is  a  red,  blue,  green,  etc., 
of  the  n  +  i  order,  for  which  the  value  may  be  looked  up  in  a 
color  chart. 

If  at  the  position  of  compensation  the  mineral  is  removed  the 
color  given  by  the  wedge  alone  should  be  that  shown  by  the 
mineral  alone  and  the  wedge  may  be  gradually  withdrawn  and 
the  color  repetition  used  as  a  check. 

The  wedges  most  used  are : 

The  Quartz  Wedge. — A  thin  wedge-shaped  plate  of  quartz  mounted  between 
glasses  and  usually  showing  four  orders.  The  values  of  A  for  different  places  may  be 
shown  on  a  scale. 

The  von  Federow  Mica  Wedge. — Composed  of  fifteen  quarter  undulation  mica 
plates  superposed  in  equivalent  position,  but  each  about  2  mm.  shorter  than  the 
one  beneath  it.  Each  plate  compensates  by  140  /JL/JL.  If  n  plates  are  needed  to  render 
the  field  dark  then*  A  =  n  X  140. 

Many  more  elaborate  compensators  exist  such  as  the  Babinet  compensator,  the 
Michel  Levy  comparator,  the  Wright  combination  wedge,  with  which  A  may  be 
determined  within  a  few  ///*.  Usually  they  cannot  be  attached  to  the  simple  micro- 
scope. 

Bands  of  interference  colors  on  wedge-shaped  outer  portions  of 
fragments  may  be  counted,  giving  thus  approximately  the  color 
order. 

*  Weinschenck  recommends  running  down  to  sensitive  violet  No.  I,  A  =  5  75  MM- 
This  value  would  then  be  added  to  the  value  of  A  interposed. 

f  That  is,  if  one  step  is  dark  and  the  two  adjacent  steps  equally  bright,  A  = 
n  X  140,  but  if  no  step  is  dark  and  two  adjacent  are  equally  bright  the  value  is 
intermediate. 


CR  Y  STALL  O-  OPTICS.  1  37 

Very  low  values  of  A  (low  order  whites,  grays,  etc.)  may  be 
approximately  determined  by  use  of  test  plates,  giving  the  sensi- 
tive violet  No.  I,  A  =  575  such  as: 


The  Gypsum  test  plate.  —  A  value  as  small  as  lo/z^t  added  or  subtracted  notably 
changes  the  color. 

The  Bravais  double  plate,  consisting  of  two  halves  of  a  sensitive  violet  set  in 
opposite  direction,  is  even  more  delicate.  Originally  made  of  mica  ^  mm-  thick. 
It  is  said  to  react  for  the  double  refraction  produced  by  finger  pressure  on  a  cube  of 
glass. 

Measuring  the  Thickness  of  the  Crystal  or  Fragment. 

If  the  refractive  index  of  the  substance  is  known  the  simplest 
plan  is  to  focus  successively  on  its  upper  and  lower  surface,  using 
the  fine  adjustment  screw.  The  distance  corresponding  to  the 
movement  of  the  screw  multiplied  by  the  average  index  of  refrac- 
tion of  the  substance  is  the  thickness.*  This  is  the  de  Chaulnes 
method,  p.  131. 

If  the  section  is  loose  a  mark  may  be  made  on  an  object  glass 
and  focused,  then  the  section  slid  on  and  the  fine  adjustment 
turned  until  some  point  on  the  surface  is  in  focus.  This  is  inde- 
pendent of  the  index  of  refraction. 

The  error  diminishes  with  increasing  thickness;  with  thin  sec- 
tions it  will  probably  be  ten  per  cent. 

Determining  the  "  Birefringence." 

The  quotient  obtained  by  dividing  the  retardation  by  the 
thickness  t  is  the  strength  of  the  double  refraction  of  that  section. 
It  is  only  that  of  the  crystal  when  the  section,  as  before  stated, 
is  parallel  to  the  optic  axis  (uniaxial)  or  plane  of  the  optic  axes 
(biaxial)  . 

Approximate  Determinations  of  Birefringence  in  Terms  of  Color. 

It  is  sometimes  convenient  to  classify  fragments  or  sections 
of  approximately  constant  thickness  by  their  birefringence  ex- 
pressed in  terms  of  color.  For  instance,  for  crushed  fragments  or 
sections  five  color  terms  can  easily  be  used.  The  terms  of  color, 
and  the  equivalent  birefringences  for  a  thickness  0.035  mm.,  and 
the  detail,  or  effect,  of  the  test-plates  may  be  stated  as  follows: 

*  If  small  basal  cleavages  of  barite  are  placed  at  the  corners  of  the  slide  and 
ground  down  with  it,  their  interference  colors  can  be  used  to  determine  the  thickness 
for  n\  —  n  =  .01,  hence  t  =  A/.oi  =  looA. 


138  CRYSTALLOGRAPHY. 

Equivalent 
Terra  of  color.  Detail.  Birefringence. 

BLACK Unchanged  by  rotation o 

GRAY  OR  WHITE  ...  By  gypsum  plate  made  yellow  for  crossed 
position,  blue  or  purple  for  parallel 
position <  0.008 

BRIGHT  A By  gypsum  plate  made  white  or  gray  or 

black  for  crossed  position 0.008  to  0.024 

BRIGHT  B By  gypsum  plate  bright  colors  for  both 

positions.  By  mica  plate  notably  dif- 
ferent tints  for  crossed  and  parallel 
positions 0.024  to  0.06 

HIGH  ORDER Not  describably  affected  by  mica  plate  in 

either  position >  0.06 

The  term  ''Bright"  signifies  definite,  brilliant  colors.  "High 
order"  signifies  faint  varied  tints  not  easily  distinguished,  and 
grading  into  white.  Bright  A  are  the  lower-order  bright  colors 
reducible  to  whites,  etc.,  by  the  gypsum  plate. 

Abnormal  Interference  Colors. 

Strictly  the  birefringence  of  a  doubly  refracting  substance, 
while  often  more  constant  than  the  indices  of  refraction,  is  not  the 
same  for  all  colors. 

In  some  minerals  it  is  zero  for  certain  wave-lengths.  If,  as 
with  vesuvianite  and  chlorite,  for  instance,  it  is  near  zero  for  yellow, 
a  deep  blue  appears  no  matter  what  the  thickness  of  the  slide. 
Other  minerals  show  other  abnormal  colors. 

The  color  of  the  mineral  itself  may  modify  the  interference 
color  and  in  some  monoclinic  or  triclinic  crystals  a  modification 
results  because  the  colors  have  no  constant  positions  of  darkness. 

DETERMINING    EXTINCTION   ANGLES   BETWEEN    CROSSED    NICOLS. 

As  explained,  p.  I  n,  when  either  of  the  two  rays  emerging  from 
a  crystal  section  is  parallel  to  the  vibration  direction  of  the  lower 
nicol  the  field  is  dark. 

The  angle  between  this  direction  and  some  recognizable  crys- 
talline direction,  cleavage,  crack,  face,  twin  plane,  etc.,  is  called 
the  extinction  angle  of  the  section. 

General  Method. 

Place  the  section  on  the  stage  of  the  microscope,  focus  with  the 
upper  nicol  out,  make  some  characteristic  crystalline  direction 


CR  YSTALL  O-  OPTICS.  1 39 

coincide  with  a  cross  hair,  read  the  vernier,  push  in  the  upper 
nicol  and  rotate  the  stage  of  the  microscope  until  the  field  is  at 
its  maximum  darkness.  Again  read  the  vernier.  The  difference 
between  the  two  readings  is  the  extinction  angle  of  the  section 
with  the  chosen  direction. 

Because  of  the  gradual  change  from  light  to  darkness  the  recog- 
nition of  maximum  darkness  is  difficult  and  if  a  closer  determina- 
tion is  desired,  the  average  of  a  number  of  measurements  taken 
as  follows  may  be  used. 

After  carefully  determining  the  position  of  the  crystalline  direc- 
tion rotate  the  stage  clockwise  until  the  field  is  dark  at  some 
reading  a.  Continue  the  rotation  until  the  field  is  light,  then 
turn  back  counter  clockwise  to  some  reading  of.  The  reading 
halfway  between  is  near  maximum  darkness. 

With  colorless  crystals  the  determination  may  be  verified  by 
slightly  rotating  the  upper  nicol.  If  the  installation  is  accurate 
the  field  and  the  crystal  will  brighten  simultaneously,  retaining 
the  same  tone. 

Sensitive  Tint  Plates. 

If  the  gypsum  test  plate,  p.  137,  or  a  quartz  plate  yielding 
sensitive  violet  No.  I  is  inserted  in  the  slot  above  the  objective 
and  the  grain  or  section  adjusted  to  only  partly  cover  the  field,  the 
entire  field  will  be  violet  for  the  extinction  positions  but  the  slight- 
est rotation  will  change  the  color  of  the  mineral  to  purple  or  indigo. 

The  Bravais  double  plate,  p.  137,  will  do  this  with  even  greater 
delicacy  one  half  becoming  purple,  the  other  indigo. 

Many  other  devices  exist  also  involving  color  contrasts  de- 
veloped when  the  vibration  directions  of  the  fragment  and  the 
nicols  are  nearly  but  not  quite  parallel. 

To  all  of  these  are  two  strong  objections. 

1.  They  are  not  available  for  monochromatic  light. 

2.  They  transmit  only  a  small  percentage  of  the  light  and  are 
effective  only  for  crystal  sections  which  are  light  in  color  and  which 
themselves  yield  the  low  colors  of  the  first  order. 

Special  Points  Extinction. 

In  tetragonal,  hexagonal  and  orthorhombic  crystals,  the  vibra- 
tion directions  coincide  with  the  crystal  axes  for  light  of  any  wave- 


140 


CR  YS  TALL  O  GRA  PHY. 


length.  Hence  white  light  is  used  and  in  general  the  extinction 
direction  will  be  parallel  or  symmetrical  to  observed  crystalline 
directions. 

In  monoclinic  crystals  the  maximum  and  characterizing  extinc- 
tion angles  are  obtained  in  sections  parallel  to  the  plane  of  sym- 
metry.* Moreover,  because  the  vibration  directions  are  different 
for  light  of  different  wave-length  monochromatic  light  should  be 
used. 

DETERMINING    UNIAXIAL   OR    BIAXIAL    BY  INTERFERENCE    FIGURES. 
The  optical  properties  of  a  crystal  may  be  studied,  not  only  in 
one  direction  but  simultaneously  in  a  great  number  of  different 
directions,  by  use  of  convergent  polarized  light. 

With  the  polarizing  microscope  select  by  parallel  light  a  suitable 
grain  or  section,  either  one  that  shows  darkness  between  crossed 
nicols  for  a  complete  rotation  or  one  that  retains  a  uniform  illumi- 
nation throughout  or  failing  these  a  grain  which  for  a  given  thick- 
ness shows  the  lowest  interference  color  (that  is,  is  nearest  normal 
to  an  optic  axis). 

This  grain  is  then  carefully  focused,  using  a  high  power  objective 
and  the  condensing  lens  directly  under,  the  stage.  The  upper 
nicol  is  pushed  in,  the  eye  piece  removed,  and  the  interference 
figure  viewed  by  looking  down  the  tube. 

The  interference  figure  thus  seen  is  made  by 
the  objective  ajone,  these  images  are  small  but 
often  sharply  defined,  the  removal  of  the  eye 
piece,  however,  makes  it  impossible  to  measure 
the  distance  between  the  axial  points  in  any 
biaxial  figure.  A  magnified  imagef  can  be  ob- 
tained if  the  eye  piece  is  retained  and  the  Bert- 
rand  lens  inserted  in  the  microscope  tube  as  de- 
scribed, p.  123. 

What  has  happened  may  be  briefly  explained 
as  follows: 

In  Fig.  261  the   foci  of  the  objective  0  and 

*  This  plane  being  always  parallel  or  perpendicular  to  the  plane  of  the  optic  axes 
can  be  found  by  convergent  light  tests. 

t  The  image  can  also  be  seen  through  the  eye  piece  by  means  of  a  hand  glass 
held  a  little  above  it. 


FIG.  261. 


'  ~m         t       i**"**  L  & 


CR  Y STALL  O-  OPTICS. 


141 


the  condensing  lens  L  coincide  at  /.  Every  point,  p,  q  or  r,  in  the 
focal  plane  F  is  the  vertex  of  a  cone  of  rays  which  is  made  parallel 
by  L,  traverses  the  crystal  as  a  parallel  bundle  and  is  by  0'  again 
brought  to  focus  at  points  p'q'r'  of  the  focal  plane  Ff.  Each  di- 
rection in  the  crystal  plate  therefore  is  traversed  by  a  minute 
bundle  of  parallel  rays,  which  undergo  the  same  extinction  and 
interference  phenomena  as  were  described  for  parallel  light,  and 
record  them  at  some  point  in  the  focal  plane  Ff. 

Every  point  of  the  image  formed  in  the  focal  plane  F'  therefore 
corresponds  to  a  direction  in  the  crystal  and  is  dark  four  times  in 
a  revolution  and  of  a  specific  color  at  all  other  times.  The  image 
is  known  as  the  "interference  figure,"  the  shape,  brightness  and 
tints  of  which  depend  upon  the  structure  of  the  plate  for  all  the 
directions  traversed  by  the  rays. 

The  results  obtained  differ  as  the  crystal  is  isotropic,  uniaxial 
or  biaxial. 

Isotropic. — The  section  which  remained  dark  throughout  rota- 
tion in  parallel  polarized  light  between  crossed  nicols  still  remains 
dark. 

UNIAXIAL   INTERFERENCE   FIGURES. 

The  section  which  remained  dark  throughout  rotation  in  paral- 
lel polarized  light  between  crossed  nicols  is  at  right  angles  to  the 


FIG.  262. 


FIG.  263. 


optic  axis.  It  does  not  remain  dark  in  convergent  light  but 
develops  the  characteristic  interference  figure,  Fig.  262,  which 
consists  of 


142  CRYSTALLOGRAPHY. 

1.  A  dark  cross,  tne  arms  of  which  intersect  in  the  center  of 
the  field,  and  remain  parallel  to  the  vibration  directions  of  the 
nicols  during  rotation  of  the  fragments. 

This  cross,  sometimes  called  the  isogyres,  corresponds  to  the 
emerging  rays  which  for  any  one  position  of  the  stage  have  their 
vibration  planes  parallel  to  the  nicols.  As  the  stage  is  rotated  suc- 
cessive rays  come  into  these  positions,  maintaining  the  same  effect. 

2.  With  monochromatic  light  the  field  will  be  of  the  color  used, 
but  if  the  section  is  not  too  thin,*  the  center  of  the  black  cross 
will  be  surrounded  by  concentric  dark  circles. 

Suppose  a  cone  of  polarized  monochromatic  light  passed  through 
the  plate  with  its  axis,  parallel  to  the  optic  axis.  The  ray  in  the 
direction  of  the  axis  will  pass  through  unchanged  and  be  stopped 
by  the  analyzer.  All  oblique  rays  at  some  particular  angle  will 
have  a  phase  difference  equal  one  wave-length  and  therefore  will 
yield  a  circle  of  darkness.  The  rays  at  some  larger  angle  will 
have  a  phase  difference  equal  two  wave-lengths  and  yield  a 
second  concentric  circle  of  darkness  and  so  on. 

With  white  light  the  concentric  circles  will  be  color  rings, 
arranged  strictly  in  the  order  of  the  interference  colors. 

Oblique  Sections. 

From  sections  which  in  parallel  light  were  not  black  but  showed 
the  lowest  obtainable  interference  color,  an  eccentric  interference 
figure  may  be  obtained,  Fig.  263.  The  center  of  the  figure 
revolves  as  the  stage  is  rotated  but  the  arms  of  the  black  cross 
remain  parallel  to  the  vibration  planes  of  the  nicols,  unless  the 
obliquity  is  great  when  they  may  be  curved. 

If  the  Birefringence  is  Weak. 

There  may  appear  only  the  black  cross  and  no  rings  which 
may  be  so  hazy  that  the  existence  of  a  figure  is  best  proved  by 
using  the  gypsum  test  plate  in  which  case  two  opposite  quadrants 
will  be  colored  blue  and  two  orange. 

*  In  uniaxial  crystals  in  which  the  optic  axis  is  a  direction  of  circular  polarization 
the  interference  figures  from  thin  sections  are  essentially  as  described  but  in  thicker 
sections  the  bars  do  not  reach  the  center  and  the  inner  circle  has  that  color  tint  which 
the  entire  section  would  have  with  parallel  light.  On  turning  the  analyzer  this  color 
will  change  in  an  order  dependent  on  the  direction  of  rotation  produced  by  the  sub- 
stance. 


CR  YSTALL  O-  OPTICS. 


BIAXIAL  INTERFERENCE  FIGURES. 

Sections  Perpendicular  to  Acute  Bisectrix.* 

When  obtainable  a  section  equally  inclined  to  both  optic  axes, 
that  is,  normal  to  the  acute  bisectrix  yields  the  following  very 
characteristic  figure : 

i.  Whatever  the  position  of  the  plate  the  "isogyres"  ap- 
pear as  two  dark  bars  or  brushes  which  correspond  to  the 
emergence  of  rays  with  their  vibration  planes  parallel  to  those 
of  the  nicols.  They  are  not  constant  in  shape.  For  the  so-called 
normal  position  one  connects  the  points  of  emergence  of  the  optic 
axes,  the  other  is  a  thicker,  lighter  band  at  right  angles  to  the 
first  and  midway  between  the  axes. 

FIG.  264.  FIG.  265. 


If  the  stage  is  rotated,  other  rays  vibrate  parallel  to  the  nicols 
and  the  straight  dark  lines  seem  to  dissolve  into  an  hyperbola  the 
poles  of  which  are  the  loci  of  the  optic  axes  and,  Fig.  266,  the 
branches  of  which  rotate  in  the  opposite  direction  to  the  rota  ton 
of  the  stage.  The  convex  side  of  each  is  always  toward  the  other 
branch. 

The  Isogyres  can  always  be  graphically  found  as  follows: 

The  directions  of  vibration  of  any  pair  of  emerging  rays  can  be  found  by  bisecting 
the  angles  between  the  two  lines  formed  by  connecting  the  point  with  the  loci  of 
the  optic  axis. 

The  isogyres  result  by  connecting  those  points,  the  vibrations  at  which  are 
parallel  to  the  vibrations  of  the  nicols. 

*  To  determine  the  acute  bisectrix  it  may  be  necessary  to  first  measure  the  axial 
angle.  Ordinarily  the  interference  figure  in  a  section  normal  to  the  obtuse  bisectrix 
will  resemble  the  figure  parallel  to  plane  of  optic  axes,  Fig.  267,  and  the  axial  loci 
will  not  be  visible. 


1 44  CRYS  TALL  O  GRAFHY. 

Thus  in  Fig.  264,  let  L  and  Lf  be  the  points  of  emergence  of  the  optic  axes.  PPf 
and  A  A'  the  vibration  directions  of  polarizer  and  analyzer  respectively,  then  the 
hyperbolae  through  L  and  U  are  the  isogyres  because  connecting  any  point  as  a,  c, 
d  or  e  with  L  and  L'  the  bisectors  are  parallel  PP'  on  A  A'  whereas  for  other  points 
of  the  field  such  as  b  the  bisectors  are  not  parallel  these  directions. 

Many  points  near  the  hyperbola  give  bisectors  nearly  parallel  PP'  and  A  A', 
therefore  at  these  there  is  approximate  extinction  resulting  in  a  broad  brush  rather 
than  a  sharp  line. 

2.  With  convergent  monochromatic  light  there  will  be,  in  a 
field  of  the  color  used,  black  closed  curves  around  the  loci  of  the 
optic  axes  corresponding  to  retardations  of  one,  two,  three,  etc., 
wave-lengths.  These  curves  will  not  be  circles  but  ovals  which 
corresponding  to  bases  of  cones  until  some  pair  unite  at  or  near 
the  center  to  a  cross  loop  or  figure  eight  around  both  axes  and 
subsequent  rings  form  lemniscates  around  this  as  in  Fig.  265. 
The  shapes  of  these  curves  do  not  change  on  rotation  of  the  plate. 

•      FIG.  266.  FIG.  267. 


If  white  light  is  used  the  superimposed  interference  figures  may 
be  much  more  complex  as  neither  the  axial  loci  nor  the  isogyres 
nor  the  cones  of  equal  retardation  coincide,  and  upon  the  changes 
in  the  isochromatic  curves  during  the  rotation  rest  important 
distinctions  between  crystalline  systems. 

Sections  Perpendicular  to  an  Optic  Axis. 

Sections  which  remain  uniformly  illuminated  with  parallel 
polarized  light  between  crossed  nicols  are  at  right  angles  to  an 
optic  axis  and  yield  an  interference  figure  somewhat  like  the 
uniaxial  figure.  The  black  cross,  however,  is  replaced  by  a  single 


CR  YSTALL  O-  OPTICS. 


black  bar,  essentially  straight,  Fig.  268,  whenever  the  trace  of 
the  plane  of  the  optic  axes  coincides  with  the  vibration  direction 
of  other  nicols.  For  all  other  angles  of  rotation  it  is  curved  and 
resembles  one  arm  of  an  hyperbola  through  the  axis,  Fig.  269, 
the  convex  side  toward  the  other  axis.  This  arm  rotates  in  the 
opposite  direction  to  the  rotation  of  the  stage. 


FIG.  268. 


FIG.  269. 


Oblique  Sections. 

The  sections  which  in  parallel  light  between  crossed  nicols  yield 
the  lowest  interference  colors  show  figures  something  like  those 
just  described.  The  single  black  bar  which  rotates  in  the  opposite 
direction  to  the  stage  proves  the  biaxial  character. 

Sections  Parallel  to  the  Plane  of  the  Optic  Axes. 

Such  sections  yield  in  monochromatic  light  an  interference 
figure,  Fig.  267,  not  easily  distinguishable  from  that  given  by  a 
uniaxial  plate  cut  parallel  to  the  optic  axis. 

DETERMINING  THE  CHARACTER  OF  THE  DOUBLE  REFRACTION. 

Optical  Character  of  Uniaxial  Crystals  in  Parallel  Light. 

If  the  direction  of  the  optic  axis  is  known  from  the  shape  of  the 
crystal  or  otherwise,  the  ray  vibrating  parallel  to  it  is  the  extra- 
ordinary. Or  if  determinations  on  several  fragments  yield  one 
constant  index  of  refraction  (ordinary)  and  one  varying  (extra- 
ordinary), then  the  character  results  by 
(+).  The  ordinary  or  constant  index  is  less  than  the  extraordinary 

or  varying  index. 
(  — ).  The  constant  index  is  greater  than  the  varying  index. 

No  corresponding  test  exists  for  biaxial  crystals, 
ii 


146 


CR  YSTALLOGRAPHY. 


Uniaxial  Crystals  with  Convergent  Light. 

The  interference  figure,  Fig.  262,  is  changed  characteristically 
by  test  plates  inserted  in  the  slot  above  the  objective. 

The  Quarter  Undulation  Mica  Plate  inserted  with  its  vibration 
directions  diagonal  to  those  of  the  nicols  breaks  the  color  rings 
into  quadrants,  and  breaks  the  cross  at  the  center  developing  two 


FIG.  270. 


FIG.  271. 


black  spots.  The  relative  effects  in  positive  and  negative  crystals 
are  shown  in  Figs.  270,  271,  the  arrow  being  the  vibration  direc- 
tion Z  of  the  slower  ray  of  the  mica  plate.  The  corresponding 
signs  -f-  and  —  are  suggested  by  the  relative  position  of  these  dark 
spots  and  the  direction  Z. 

If  the  Gypsum  Test  Plate  is  similarly  inserted  the  black  cross 
becomes  reddish  violet  and  near  the  center  two  opposite  quadrants 
become  blue,  the  other  two  yellow. 

If  a  line  be  assumed  to  join  the  blue  quadrants  this  line  in 
positive  crystals  crosses  the  direction  of  vibration  X  and  in 
negative  crystals  is  parallel  to  it,  again  suggesting  the  correspond- 
ing +  and  —  signs. 

Uniaxial  Oblique  Sections. 

Rotate  the  plate  until  only  one  quadrant  of  the  figure  is  in  the 
field,  judge  the  position  of  the  center  of  the  cross  by  the  arms  or 
curvature  of  the  color  rings,  insert  the  mica  and  note  the  position 
of  the  shifting  color  arcs  or  of  any  developed  dark  spot  with 
reference  to  Z  of  the  mica  plate. 

Biaxial  Sections  Normal  Acute  Bisectrix. 

In  sections  normal  the  acute  bisectrix,  the  quarter  undulation 
mica  plate  may  be  used  as  described  above,  for  uniaxial  crystals 


CR  YSTALL  O-  OPTICS. 


when  the  distance  between  the  points  of  emergence  of  the  axes  is 
small. 

The  compensating  quartz  wedge  may  be  inserted  successively 
with  Z  and  X  parallel  to  the  diagonal  line  connecting  the  axial 
points.  In  one  of  these  insertions  the  rings  around  each  axis 
will  expand,  moving  toward  the  center  and  corresponding  rings 
will  merge  in  one  curve.  When  this  direction  is  Z  the  character 
is  plus  (+),  when  the  direction  is  X  the  character  is  minus  (  — ). 

Biaxial  Sections  Showing  the  Optic  Axis. 

Sections  perpendicular,  or  nearly,  to  an  optic  axis  show  the  dark 
bar  which  is  noticeably  convex*  towards  the  acute  bisectrix.  If 
rotated  into  the  position  of  Fig.  269  and  the  gypsum  test  plate 
inserted  the  bar  becomes  violet  red  but  is  differently  bordered 
in  positive  and  negative  crystals. 

Positive  crystals  concave  side  yellow,  convex  side  blue. 

Negative  crystals,  concave  side  blue,  convex  side  yellow. 

Determining  the  Angle  between  the  Optic  Axis. 

As  stated  p.  105  the  so-called  optic  axes  of  biaxial  crystals 
are  determinable  directions  for  monochromatic  light  and  constant 


FIG.  272. 


temperature.       The    angle    between 
them  can  therefore  be  measured.* 

The  optic  axes  lie  in  the  plane  of 
X  and  Z  and  these  directions  bisect 
the  angles  between  the  axes.  Either 
however  may  be  the  acute  bisectrix 
Bxa,  Fig.  272. 

Usually  a  plane  parallel  plate  is  cut 
normal  to  the  acute*bisectrix. 

The  rays  travelling  parallel  to  the 
optic  axis  are  obliquely  incident  at  the  air  and  are  refracted, 
the  apparent  angle,  Fig.  272,  denoted  by  2E,  being  larger  than 
the  true  angle,  denoted  by  2V. \ 

Although^  a  definite  character  for  a  crystal  of  definite  com- 

*  Unless  the  axial  angle  is  very  close  to  90°. 

f  In  Fig.  272,  for  instance,  2V  =  56°,  2E  =  98°. 

t  In  orthorhombic  crystals  the  same  plate  will  be  normal  for  all  colors,  but  in  the 
other  systems  this  is  not  so,  but  if  the  plate  be  cut  normal  for  a  middle  color,  say 
yellow,  the  results  for  all  colors  will  be  approximately  accurate. 


148 


CR  YSTALLOGRAPHY. 


position  2  V  varies  widely  in  the  great  minerals  which  are  isomor- 
phous  mixtures  and  is  therefore  less  used  than  the  other  optical 
characters. 

Determining  the  Apparent  Angle  with  the  Microscope. 

The  apparent  axial  angle*  2E  may  be  determined  in  such  a  plate 
as  Fig.  272  in  any  suitably  equipped  microscope,  by  measuring 
the  distance,  2d,  between  the  points  of  emergence  of  the  optic 
axes.  Usually  the  interference  figure  is  placed  in  its  diagonal 
position,  Fig.  266,  and  the  distance  2d  measured  between  the  foci 
of  the  hyperbola  by  some  form  of  micrometer  eye  piece. 

FIG.  273. 


Then  sin  E  =  d/C,  in  which  C  is  a  constant  for  the  same  system 
of  lenses  and  is  determined  once  for  all  by  means  of  crystals  of 
known  axial  angles. 

*  The  axial  angle  can  also  be  determined  in  sections  showing  the  emergence  of 
only  one  optic  axis  by  means  of  the  curvature  of  the  isogyres  (p.  143).  (See  Johann- 
sen,  "  Petrographic  Methods,"  p.  480.) 


CR  YSTALL  O-  OPTICS.  149 

For  instance,  if  in  a  mica  2E  =  91°  50'  and  d  =  41.5  divisions  on  the  scale,  then 
C  =  d/sin  E  =  57.78  for  that  combination  of  lenses. 

Determination  of  the  Axial  Angle  by  Rotation. 

A  more  exact  measurement  may  be  made  by  actual  rotation 
of  the  plate  about  Y  as  an  axis.  The  microscope,  with  some  form 
of  rotation  apparatus,  Fig.  274,  attached,  may  be  used  or  a 
polariscope,  Fig.  273.  The  microscope  or  polariscope  is  usually 

FIG.  274. 


v.  Federow  Universal  Stage. 

horizontal  and  the  nicols  are  crossed  at  45°  to  the  horizon,  sor 
that  when  the  line  connecting  the  axial  points  is  horizontal  the 
interference  figure  shows  the  hyperbola.  The  section  is  adjusted 
so  that  the  axial  points  of  the  interference  figure  remain  on  the 
horizontal  cross  hair  during  revolution. 

The  crystal  is  then  revolved  and  the  arms  of  the  hyperbola 
are  successively  made  tangent  to  the  vertical  cross  hair.  The 
difference  between  the  two  readings  is  the  apparent  angle  2E. 

Determining  the  True  Angle. 

A  second  measurement  may  be  made  of  the  apparent  angle  in 
a  plate  normal  to  the  obtuse  bisectrix.  Denoting  this  by  2E'  the 

sinE 

relation  is  tan  V  =  - — ^  . 
sin  E 

If  the  middle  index  /3  is  known 

sinE 

smF       — 

If  the  section  is  immersed  in  a  liquid  of  index  or  even  the  mean 
index  found  by  Becke  test,  then  E  =  V. 


150  CRYSTALLOGRAPHY. 

DETERMINING    THE    CRYSTALLINE    SYSTEM    BY    OPTICAL    TESTS. 

The  crystalline  system  can  usually  be  identified  as  follows: 

If  each  grain  or  section  tested  is  Homogeneous,  that  is,  shows  in 
all  parts  the  same  optical  behavior.  Determine  by  test  page  127 
whether  isotropic  or  anisotropic. 

Anisotropic. — Confirm  by  the  fact  that  no  interference  figure 
is  produced  by  convergent  light. 

(a)  Amorphous. — Absence  of  crystalline  form  or  cleavage. 

(b)  Isometric. — Presence  of  crystalline  form  or  cleavage. 

B.  Anisotropic. — By  test  page  140  seek  out  suitable  fragment  or 
section*  and  determine  whether  uniaxial  or  biaxial. 

(a)  Uniaxial. — Confirm  by  fact  that  in  other  grains  or  sections 
extinction  always  takes  place  for  directions  parallel  or  symmetrical 
to  crystal  outlines,  cleavage  cracks,  etc.,  p.  139. 

No  purely  "optical"  distinction  exists  between  the  tetragonal 
and  hexagonal  crystals.  The  section  or  fragment  which  yielded 
the  interference  figure  may  show  outlines  or  cleavages  character- 
istic of  the  system. 

Tetragonal — Angles  of  90°  or  135°. 

Hexagonal — Angles  of  60°  or  120°. 

(b)  Biaxial,     i.  Orthorhombic. — In  the  interference  figure  ob- 
tained in  grain  or  section  normal  to  a  bisectrix  with  white  light  the 
shape  of  the  isochromatic  curves  will  be  symmetrical  to  the  line 
joining  the  optic  axes,  to  the  line  through  the  center  at  right  angles 
thereto  and  to  the  central  point. 

In  all  sections  or  grains  parallel  to  any  one  of  the  three  crystallo- 
graphic  axes  a,  b,  and  c,  the  extinction  will  take  place  with  parallel 
light  in  directions  parallel  or  symmetrical  to  cleavage  cracks  and 
crystal  outlines. 

There  may  be  two  cases  dependent  on  the  different  axial 
angles  for  light  of  different  wave-length,  and  as  the  colors 
fringing  the  hyperbola  will  be  in  inverse  position  to  the  axial 

*  Much  can  be  done  with  forms  of  rotation  apparatus.  Fig.  274  shows  the  v. 
Federow  Universal  Stage  with  three  axes  of  rotation.  The  stand  IV  carrying  the 
stage  can  be  placed  on  the  stage  of  the  microscope.  By  k  the  stage  is  rotated 
about  a  horizontal  axes,  the  amount  of  rotation  being  shown  on  T.  The  stage  K 
is  rotated  about  a  second  axis  perpendicular  to  the  first,  the  amount  being  read  on 
the  vernier  m;"it  also  carries  a  third  axis,  Hd  (a  diameter  in  its  plane).  Finally  the 
glass  plate,  S,  carrying  the  object  can  be  rotated  in  its  plane. 


CRYSTALLO-OPTICS.  151 

points.  For  red  less  than  violet,  the  red  is  further  from  the 
center  than  the  blue.  For  red  greater  than  violet,  the  red  is 
nearer  the  center  than  the  blue. 

2.  Monoclinic. — In  the  interference  figure  obtained  described 
above  with  white  light  the  shape  of  the  isochromatic  curves  will 
be  symmetrical  to  one  line  or  the  central  point.  The  line  of  sym- 
metry may  join  the  axial  points  (Inclined  Dispersion)  or  (6)  be 
at  right  angles  to  this  (Horizontal  Dispersion)  or  there  may  "be 
symmetry  to  the  center  (Crossed  Dispersion). 

In  all  grains  or  sections  parallel  to  the  axes  of  geometric  sym- 
metry extinction  will  take  place  in  directions  parallel  or  symmetrical 
to  crystal  outline  or  cleavage  cracks. 

In  all  other  grains  or  sections  the  directions  will  be  oblique  and 
unsymmetrical. 

(c)  Tridinic. — In  the  interference  figure  with  white  light  the 
isochromatic  curves  are  not  symmetrical  to  line  or  center. 

The  directions  in  which  extinction  takes  place  are  always  oblique 
and  unsymmetrical  to  crystal  outlines  or  cleavages. 

ABSORPTION,    COLOR   AND   PLEOCHROISM. 

Absorption. 

When  monochromatic  light  is  either  reflected  from  or  trans- 
mitted through  a  crystal  it  undergoes  partial  absorption,  the 
amount  absorbed  increasing  with  the  thickness. 

If  the  crystal  is  doubly  refracting  the  rate  of  absorption  will 
probably  be  different  for  the  two  rays  transmitted  in  any  direction 
and  also  different  in  different  directions. 

If  white  light,  composed  of  a  multitude  of  lights  of  different 
color  and  different  wave-lengths,  is  used  each  component  light  is 
affected  as  described,  but  the  percentages  absorbed  may  be  either 
alike  or  different  (Selective  Absorption). 
Color. 

If  the  absorption  of  all  the  colors  has  been  essentially  in  the 
same  ratio  the  body  appears  colorless  or  white.  If  not  in  the 
same  ratio,  then  it  appears  that  tint  which  results  from  the 
combined  effect  of  the  unabsorbed  portions  of  the  component 
lights. 


152  CRYSTALLO  GRA  PHY. 

The  color  depends  also  on  the  proportions*  of  the  different 
monochromatic  colors  in  the  light  used  as  a  source,  for  instance, 
alexandrite  is  red  by  candle  light,  green  by  sunlight  and  of  an 
intermediate  tint  by  a  tungsten  light.  The  substance  simply 
possesses  the  power  to  absorb  certain  tints,  that  is,  light  of  certain 
wave-lengths  more  rapidly  than  others.  The  "color"  is  what  is 
left. 

Transparency  vs.  Opacity. 

If  the  non-absorbed  rays  penetrate  the  substance  it  appears 
transparent  and  colored  or  colorless,  if  they  are  all  reflected  it 
appears  opaque,  colored  or  white.  If  all  are  absorbed  it  appears 
black. 

Pleochroism  in  General. 

In  doubly  refracting  crystals  the  color  in  different  directions 
may  be  noticeably  different  as  in  epidote  and  iolite. 

The  two  rays  transmitted  in  any  one  direction  may  also  be 
differently  colored.  Usually  the  eye  observes  a  mixed  resultant 
color. 

This  variation  in  color  is  called  pleochroism  or  dichroism.  It  is 
impossible  in  singly  refracting  material  and  in  colorless  doubly 
refracting  material.  In  colored  doubly  refracting  material  it  is 
a  common  but  not  necessary  phenomenon,  and  when  present  is 
best  displayed  by  the  deeper  colored  crystals. 

Pleochroism  in  Uniaxial  Crystals. 

The  optic  axis  is  a  direction  of  single  refraction  for  white  light 
and  pleochroism  does  not  occur  in  this  direction,  that  is,  in  sections 
normal  to  the  optic  axis  the  color  is  constant,  but  in  any  other 
section  the  two  rays  are  differently  absorbed  and  may  be  differently 
colored. 

The  color  of  one  of  these  rays  is  constant  for  a  given  thickness 
whatever  the  direction  of  the  section.  The  color  of  the  other 
varies  with  the  section  and  differs  most  from  the  constant  (ordi- 
nary) ray  in  the  section  cut  parallel  to  the  optic  axis  and  in  all 
other  sections  the  ordinary  will  be  found  to  approach  the  constant 

*  The  proportions  of  the  different  monochromatic  colors  varies  even  in  sunlight, 
and  the  differences  between  even  the  best  artificial  light  and  sunlight  are  very  great, 
the  former  usually  containing  far  greater  proportions  of  yellow  and  red. 


CR  YSTALL  O-  OPTICS.  1 53 

tint  of  the  ordinary  as  the  sections  become  more  nearly  per- 
pendicular to  the  optic  axis. 

The  relation  of  absorption  to  transmission  varies:  the  directions  of  principal  ab- 
sorption (maximum  and  minimum)  coincide  for  all  colors  with  the  principal  vibration 
directions  A'  and  Z. 

There  is  no  necessary  relation  between  degree  of  absorption  and  indices  of  refrac- 
tion and  two  classes  may  be  made. 

1.  Absorption  of  ordinary  ray  greater  than  that  of  extraordinary  ray. 

2.  Absorption  of  ordinary  ray  less  than  that  of  extraordinary  ray. 

Pleochroism  in  Biaxial  Crystals. 

A  pleochroic  biaxial  crystal  shows  pleochroism  in  all  directions. 

It  is  true  there  are  for  any  one  temperature  and  light  of  any  one  wave-length  two 
directions  of  single  refraction.  But  when  white  light  is  used  each  color  has  its  slightly 
different  direction  of  single  refraction  and  moreover  the  light  which  emerges  travelling 
in  one  of  these  directions  is  merged  with  the  doubly  refracted  light  from  an  inner  cone 
of  rays  which  after  emergence  travel  in  the  direction  of  the  optic  axis,  therefore  any 
such  composite  bundle  will  show  dichroic  effects  and  will  not  give  darkness  between 
crossed  nicols. 

It  is  customary  to  record  the  colors  obtained  for  rays  vibrating 
parallel  X,  Y  and  Z  and  where  possible  to  record  also  the  relative 
degrees  of  absorption  in  these  directions. 

The  directions  of  principal  absorption  (maximum  and  minimum)  coincide  with 
X,  Y,  Z  for  all  colors  in  orthorhombic  crystals.  They  do  not  so  coincide  in  triclinic 
crystals  nor  completely  coincide  in  monoclinic  crystals. 

There  is  no  relation  between  the  degree  of  absorption  and  the  indices  of  refraction. 
Maximum  absorption  may  be  in  the  plane  of  the  optic  axes  or  perpendicular  thereto. 

Determining  Pleochroism  with  the  Microscope. 

Minute  grains  and  fragments  as  well  as  larger  sections  may 
be  examined  as  follows:  Focus  with  the  upper  nicol  out;  push  in 
upper  nicol  and  rotate  the  stage  until  the  field  is  dark;  push  out 
the  upper  nicol  and  note  the  color  of  stone.  Rotate  the  stage  90° 
and  again  note  the  color.  These  positions  usually  give  the  maxi- 
mum difference  in  color  for  the  direction  of  transmission.  The 
pleochroism  may  appear  as  a  change  in  color  or  a  change  in  the 
shade  of  the  same  color. 

In  intermediate  positions  of  rotation  the  color  is  due  to  com- 
ponents of  each  of  the  extreme  colors,  in  the  diagonal  position 
these  components  are  equal. 

There  emerge  from  the  stone  two  rays  vibrating  at  right  angles  but  differently 
absorbed  and  possibly  colored,  but  not  sufficiently  divergent  to  be  seen  separately 
and  yield  a  combination  color. 


154 


CR  YSTALLOGRAPHY. 


If  one  can  be  held  back  the  other  can  be  seen  or  vice  versa.  When  the  lower  nicol 
of  a  microscope  is  parallel  an  extinction  direction  one  of  the  two  rays  that  gets 
through  and  its  color  is  seen.  When  the  stage  has  been  revolved  90°  the  other  ray 
gets  through  and  its  color  is  seen. 

In  intermediate  positions  the  color  is  due  to  both. 

If  it  is  desired  to  show  the  colors  side  by  side  a  dichroscopic 
ocular  may  be  used,  Fig.  275.  The  action  is  like  that  of  the 
dichroscope  described  below.  It  is  especially  applicable  to  the 
grains  in  thin  sections. 

Determining  Pleochroism  with  Dichroscope. 

The  colors  of  the  ordinary  and  extraordinary  rays  may  be  con- 
trasted side  by  side  by  means  of  a  "dichroscope,"  Fig.  276,  which 


FIG.  275. 


FIG.  276. 


1 

G/          / 

/  s  / 

i 

is  in  its  essentials  a  cylindrical  casing  with  a  rectangular  hole,  H, 
at  one  end  and  a  lens,  L,  at  the  other  and  between  a  rhomb  of 
calcite  S  of  such  a  length  that  the  two  images  of  the  hole  are 
just  in  contact. 

In  some  instruments  the  terminal  faces  of  the  rhomb  are  ground 
at  right  angles  to  its  length,  but  usually  wedges  of  glass  G  are 
attached. 

The  section  or  stone  to  be  tested  may  be  directly  attached  to  a 
movable  cap  C  by  means  of  some  kind  of  wax  or  cement  so  that 
the  light  which  has  traversed  it  passes  into  the  window,  H. 

The  instrument  shown,  Fig.  277,  has  convenient  devices  by 
which  the  crystal,  or  section,  or  cut  stone  may  be  held  and  turned 
about  two  axes,  one  at  right  angles  to  the  length  of  the  tube,  the 


CR  YSTALL  O-  OPTICS.  1 55 

other  parallel  to  the  length  of  the  tube,  and  thus  examined  in 

different  directions. 

FIG.  277. 

><£ 


The  method  of  using  is  as  follows:  Hold  the  stone  close  to  the 
square  orifice  and  rotate  the  instrument  until  the  two  images  are 
of  the  same  color.  Midway  between  two  such  positions  the  colors 
differ  most.  Whether  pleochroism  is  shown  for  this  position  or 
not,  place  the  stone  in  a  second  notably  different  position  and 
again  try  for  the  limit  colors. 

In  examining  a  cut  stone  revolve  the  dichroscope  rather  than  the 
stone  so  as  to  avoid  different  light  effects  from  different  positions 
of  facets,  and  verify  the  fact  that  the  differences  are  due  to 
pleochroism  by  noting  that  the  two  images  of  any  face  interchange 
colors  for  90°  of  rotation  of  the  dichroscope. 

The  dichroscope  does  not  produce  the  colored  rays,  they  emerge 
from  the  crystal  and  the  calcite  simply  renders  them  more  diver- 
gent so  they  can  be  seen  at  the  same  time. 

As  the  dichroscope  is  turned  each  ray  from  the  crystal  is  de- 
composed in  the  calcite  and  contributes  a  portion  of  its  intensity 
to  each  of  the  two  images,  but  at  the  positions  of  maximum 
difference  of  color  the  vibration  directions  of  the  two  rays  from 
the  crystal  and  the  vibration  directions  of  the  calcite  coincide. 


PART  II. 


BLOWPIPE  ANALYSIS 


CHAPTER  XI. 
APPARATUS,  BLAST,  FLAME,  ETC. 

Qualitative  determination  of  component  elements  and  tests 
of  fusibility  and  solubility  are  very  important  aids  in  the  identi- 
fication of  mineral  species,  and  together  with  a  limited  number 
tests  with  wet  reagents  are  here  discussed  under  the  title  of 
Blowpipe  Analysis. 

Bartholin,  the  describer  of  double  refraction,  appears  to  have 
been  the  first  to  utilize  the  blowpipe  in  mineral  testing,  for  in  1670 
he  states  that  iceland  spar  before  the  blowpipe  was  burned  to 
lime.  Kunckel  nine  years  later  recommended  its  use  in  chemical 
testing.  Its  more  systematic  use  in  mineral  testing  dates  from 
Anton  Swab  in  1733  and  was  developed  at  first  in  Sweden  by 
Gahn,  Cronstedt,  Berzelius  and  others  and  later  in  Germany  by 
Plattner,  Richter,  von  Kobell  and  Bunsen. 

The  Advantage  of  "  Blowpipe  Tests." 

Minerals  are  in  general  insoluble  in  water  and  many  of  them 
insoluble  in  acids.  Their  examination  by  wet  methods  would 
usually  require  a  previous  fusion  and  solution. 

With  the  blowpipe  the  tests  are  made  directly  upon  the  mineral, 
and  are  rapidly  obtained,  with  very  little  material  and  with  very 
simple,  easily  portable  apparatus  and  reagents. 

Although  group  separations,  except  for  instance  into  volatile 
and  non-volatile,  are  not  practicable  the  order  of  testing  is  not 
indifferent  as  it  is  often  desirable  that  certain  elements  be  detected 
and  largely  removed  before  making  the  tests  for  the  others. 

156 


APPARATUS,    BLAST,    FLAME. 


157 


The  set  of  apparatus  which  has  been  found  best  in  the  work  at 
Columbia  University  consists  of  the  following  articles  : 

1  Streak   plate    (fine   grained)    E   &   A 

5310,  size  2  1/8"  x  3  3/8". 

2  Ft.   rubber   tubing,    1/8"    I    D,    pure 

gum,  E  &  A  6052. 
i  Dropping  tube,  pipette,  small,  E  &  A 

5224, 
6  Reagent  bottles  in  wood  block,  with 


i  Gas  blowpipe,  Plattner's,  E  &  A  No 

794,  modified, 
i  Forceps,     platinum     tipped,     French 

style,  E  &  A  3206. 
i  Cupel    holder,    2    moulds,    i    stamp, 

E  &  A  829,  made  more  convex  by 

Columbia, 
i  Steel  hammer,  Colton's,  wire  handled, 

E  &  A  3820. 
i  Leed's  Diamond  mortar,  E  &  A  4628, 

in  wooden  box. 
i  Chisel    and     borer     (combined)     not 

magnetized,  E  &  A  817. 
i   Bar   magnet   in   iron   case,    one   end 

bevelled,  Columbia  make, 
i  Coal  tray,  E  &  A  853,  but  size  5^"  x 

41A". 

6  Watch  glasses,  2"  E  &  A  7832. 
12  Closed  tubes — sublimation,  closed  at 

one  end,  O  D  8  mm.,  I  D  6  mm., 

length  TOO  mm.     J.  Kavalier's  hard 

Bohemian  combustion  tubing. 

The  Blowpipe 


special  short  corks  in  bottles. 
3  Pieces  charcoal,  willow,  close  grained, 

best  grade. 

i  Holder  for  platinum  wire,  E  &  A  831. 
i   Platinum  wire  (6  inches)  B  &  S  No.  28. 
i  Outfit  box,  for  carrying  apparatus. 
6  Inch  white  rubber  tubing,  3/16"  I  D. 
i   Box  for  hardness  scale — New  England 

Box  Co. 
i  Merwin's  flame  color  screen — G.  M. 

Flint,  Cambridge,  Mass, 
i  Penfield    contact    goniometer,    model 

B,  Sheffield  Scientific  School, 
i  Coddington    lens,     loX,     Bausch    & 

Lomb  No.  162. 
i  File,  i/8"x3"xi/8". 


The  best  form  of  blowpipe  (Fig.  278)  consists  of: 

1.  A  tapering  tube  of  brass  or  German  silver  (B),  of 
a  length  proportionate  to  the  eyesight  of  the  user. 

2.  A  horn  or  hard  rubber  mouthpiece  (C)  at  the  larger 
end   of  the  tube.     This  should   be  of  trumpet-shape  to 
fit  against  the  lips. 

3.  A  moisture  chamber  (A)  at  the  smaller  end  of  the 
tube  connected  by  ground  joints  to  : 

4.  A  tapering  jet  (£)  at  right  angles  to  the  moisture 
chamber. 

5.  A   tip  of  platinum   or  brass  (c\   shown   enlarged, 
which  should  be  bored  from  a  solid  piece,  and  with  an 
orifice  of  o.  5  millimeter  diameter.     The  tip  is  by  far  the 
most  important  part  of  the  blowpipe,   and,   if  correctly 
made,  the  flame  produced  will   be  perfectly  regular  and 

will  not  flutter. 

When  not  in  use  the  blowpipe  should  be  so 
placed  that  the  tip  is  supported  free  from  con- 
tact. If  the  tip  is  clogged  by  smoke  or  other- 
wise is  should  be  burned  out  or  cleaned  with 
the  greatest  care  so  as  not  to  injure  the  regu- 
ular  form  of  the  orifice. 


158 


BLOWPIPE  ANALYSIS. 


Gas  Blowpipe. 

For  most  purposes  the  gas  blowpipe,  Fig.  279,  is  a  convenient 
form  and  is  extensively  used.  The  flame  is  not  quite  so  hot  as 
that  from  rape-seed  oil,  but  is  sufficient  to  round  the  edges  of  a 
calamine  splinter.  Oxidation  and  reduction  are  easily  obtained 
and  the  cleanliness  and  ease  of  control  cause  it  to  be  preferred  by 

FIG.  279. 


many.     The  ordinary  blowpipe  can  be  made  into  a  gas  blowpipe 
by  means  of  an  attachment  to  connect  to  the  moisture  chamber. 

Blowpipe  Lamps. 

Bunsen  Burner.  —  The  simplest  form  of  lamp  for  laboratory  pur- 

FIG.  280.  FIG.  281. 


poses  is  the  ordinary  Bunsen  burner,  Fig.  280,  using  gas  and  fur- 
nished with  a  special  top  («),  or  an  inner  tube  shaped  to  spread 


APPARATUS,    BLAST,    FLAME. 


159 


the  flame.  When  used  with  the  blowpipe  the  orifices  (&)  at  the 
bottom  of  the  burner  should  be  closed,  so  that  no  air  enters  with 
the  gas.  A  flame  about  4  cm.  high  gives  the  best  results. 

The  hottest  flame  and  greatest  variations  in  quantity  and  quality 
of  flame  are  obtained  from  oils  rich  in  carbon,  such  as  refined  rape- 
seed,  or  olive  or  lard  oil,  or  from  mixtures  of  turpentine  and  alco- 
hol. These  can  be  used  in  the  field  and  where  gas  is  not  available. 
In  some  kinds  of  blowpipe  work  they  are  to  be  preferred  to  gas, 
but  will  not  serve  for  bending  glass  or  for  heating  without  the 
blowpipe. 

Berzelius  Lamp.  — A  lamp  with  two  openings,  Fig.  281,  is  gen- 
erally used  for  oil. 

The  wick  should  be  soft,  close-woven  and  cylindrical,  such  as 
is  used  with  Argand  lamps.  It  should  be  folded  and  inserted  with 
the  opening  toward  the  lower  side  of  the  brass  holder. 

To  fill  the  lamp  both  caps  are  removed  and  the  oil  poured  in 
through  the  smaller  orifice.  During  work,  the  smaller  cap  is  hung 
on  the  vertical  rod  ;  the  larger  is  placed  over  the  smaller  orifice 
loosely,  keeping  out  the  dust,  but  admitting  the  needed  air. 

The  lamp  is  lighted  by  blowing  a 
flame  up  and  across  the  wick.  When 
well  charred,  the  wick  is  carefully 
trimmed  parallel  to  the  brass  holder. 

Fletcher  Lamp.  —  The  Fletcher  blow- 
pipe lamp,  Fig.  282,  gives  good  satisfac- 
tion, and  a  modified  form,  burning  solid 
fats,  tallow  or  paraffine,  is  especially 
adapted  for  field  work. 


Supports  of  Charcoal,  Plaster,  Etc. 

Charcoal.  —  Charcoal  made  from  soft  woods,  such  as  willow  or 
pine,  is  used  to  support  the  substance  and  receive  any  coats  or 
sublimates  that  may  form,  and,  in  a  measure,  is  a  reducing  agent. 
A  convenient  size  is  4  inches  long,  I  inch  broad,  and  ^  inch  thick. 

Plaster.  —  Plaster  tablets  are  used  for  the  same  purpose.  These 
are  prepared  by  making  a  paste  of  plaster  of  Paris  and  water,  just 
thick  enough  to  run,  which  is  spread  out  upon  a  sheet  of  oiled 
glass  and  smoothed  to  a  uniform  thickness  (  V^"  to  %")  by  another 
smaller  sheet  of  glass,  which  may  be  conveniently  handled  by  gum- 
ming a  large  cork  to  one  side  and  using  it  as  a  plasterer's  trowel. 


FIG.  282. 


160  BLOWPIPE  ANALYSIS. 

While  still  soft,  the  paste  is  cut  with  a  knife  into  uniform  slabs, 
4"  by  \y2".  It  is  then  dried,  after  which  the  tablets  are  easily 
detached. 

FORCEPS,  with  platinum  tips  for  fusion  tests.     The  most  con- 

FIG.  283. 


venient  form  is  shown,  Fig.  283,  the  platinum  ends  projecting  at 
least  three  fourths  of  an  inch. 

PLATINUM  WIRE  AND  HOLDER. — Wire  of  the  thickness  of  about 
one  quarter  millimeter  and  a  holder  in  which  the  wires  can  be 
changed  and  with  a  receptacle  for  a  stock  of  wires. 

CLOSED  AND  OPEN  TUBES.     See  Figs.  296  and  297. 

CUPEL  HOLDER  AND  CUPELS,  for  silver  determination.  See 
Figs.  403  and  404. 

Miscellaneous  Apparatus : 

REAGENT  BOTTLES. — Eight  2-oz.  wide-mouthed  bottles;  for 
borax,  soda,  salt  of  phosphorus,  and  bismuth  flux  will  be  needed 
at  all  times  in  a  convenient  stand. 

ANVIL. — Slab  of  polished  steel,  about  \\"  by  i\"  by  J",  or 
better  a  Leeds  diamond  mortar,  Fig.  284. 

HAMMER. — Steel,  with  square  face,  -|"  or  i";  the  most  satisfac- 
tory being  the  Colton  with  wire  handles,  Fig.  285. 

FIG.  284.  FIG.  285. 


Other  important  pieces  of  apparatus  are :  bar  magnet,  with 
chisel  edge ;  trays,  for  dirt  and  for  charcoal ;  lens  and  watch 
glasses  ;  cutting  pliers ;  small  porcelain  dishes,  ivory  spoon  and 
dropping  tube. 

Very  useful  accessories  are  the  Merwin  Color  Scale,  p.  165  ;  a 
Hardness  Scale,  p.  217,  and  a  Penfield  Goniometer,  Fig.  I. 


APPARATUS,    BLAST,    FLAME. 


161 


BLAST   AND  FLAME. 

The  Blast. 

The  blast  is  produced  by  the  muscles  of  the  distended  cheeks, 
and  not  by  the  lungs. 

It  is  best  to  sit  erect,  with  the  blowpipe  held  lightly  but  firmly 
in  the  right  hand,  and  with  the  elbows  against  the  sides.  Then, 
with  the  cheeks  distended  and  the  mouth  closed,  place  the  mouth- 
piece against  the  lips,  breathe  regularly  through  the  nose,  and 
allow  air  to  pass  into  the  pipe  through  the  lips.  From  time  to 
time,  as  needed,  admit  air  to  the  mouth  from  the  throat.  In  this 
manner,  after  learning  to  breathe  through  the  nose  while  keeping 
the  cheeks  distended,  a  continuous  blast  can  be  blown  without 
fatigue. 

The  Flame. 

A  LUMINOUS  FLAME  (Fig.  286)  usually  shows  three  distinct  por- 
tions. 

1.  A  very  hot  non-luminous  veil,  a,  of  carbon 
dioxide  and  free  oxygen. 

2.  A  yellow    luminous    mantle,   b,    of  burning 
gases  and  incandescent  carbon. 

3.  An  interior  dark  cone,  c,  of  unburned  gases, 
not  always  visible. 

Oxidation  and  Oxidizing  Flame. 

The  oxidizing  flame  is  non-luminous,  for  lumi- 
nosity indicates  unconsumed  carbon,  and  hence  a 
reducing  action. 

To  produce  such  a  flame,  place  the  tip  of  the 
blowpipe  almost  touching  the  top  of  the  burner, 
or  the  wick,  and  extending  in  %  the  breadth 
of  the  flame ;  blow  parallel  to  the  burner  top  or  wick  until  there 
is  produced  a  clear  blue  flame  nearly  an  inch  long.  This  blue 
flame  is  weakly  reducing,  but  just  beyond  the  blue  at  a  (Fig.  287)  is 
an  intensely  hot,  nearly  colorless  zone,  which  is  strongly  oxidizing, 
and  the  bead  is  held  in  this  usually  as  far  from  the  tip  of  the  blue 
flame  as  the  bead  can  be  kept  fluid.  If  the  substance  to  be  oxi- 
dized is  supported  on  charcoal,  a  weak  blast  must  be  used. 


12 


162  BLOWPIPE  ANALYSIS. 

With  the  gas  blowpipe  all  that  is  necessary  is  to  avoid  an  excess 
of  gas.  The  blue  flame  is,  as  before,  surrounded  by  the  oxidizing 
colorless  mantle. 

Purity  of  Oxidizing  Flame  by  Action  on  Mo03. 

Regulate  the  supply  of  gas  until  the  blowing  produces  a  clear 
blue  flame  nearly  an  inch  long.  This  blue  flame  itself  is  weakly 
reducing,  but  is  surrounded  by  an  intensely  hot,  nearly  colorless 
zone,  which  is  strongly  oxidizing.  The  bead  is  held  in  the  latter, 
Fig.  287,  as  far  out  from  the  tip  as  it  will  keep  fluid. 

Make  a  loop  in  platinum  wire  by  bending  it  around  a  pencil 
point  so  that  the  end  meets  but  does  not  cross  the  straight  part, 

FIG.  287.  FIG.  288. 


Fig.  288.  Heat  the  loop,  dip  it  into  borax  and  fuse  the  portion 
that  adheres  to  a  clear  bead.  Add  more  borax  until  the  bead  is  of 
full  rounded  shape. 

Dip  the  hot  bead  into  the  MoO3,  dissolve  the  adhering  material 
at  the  tip  of  the  blue  flame  and  make  the  bead  alternately  brown 
or  black  from  MoO2  and  colorless  from  MoO3  by  varying  the  posi- 
tion of  the  bead  in  the  flame. 

Purity  of  Reducing  Flame  by  Action  on  Mn02. 

Regulate  the  gas  to  produce  a  larger  flame  than  for  the  pre- 
ceding test.  This  may  be  so  done  that  during  the  blast  there 
is  still  a  distinctly  yellow  part  near  the  end  of  the  flame. 
The  bead  should  be  kept  covered  by  this  yellow  portion,  Fig. 
289. 

The  blast  must  be  continuous ;  too  strong  to  produce  a  sooty 
flame,  and  not  strong  enough  to  oxidize  by  excess  of  air. 

The  blue  flame  also  is  reducing  because  of  the  carbon  monoxide 
it  contains,  but  it  is  not  as  effective. 


APPARATUS,    BLAST,    FLAME. 


Make  a  borax*  bead  as  in  the  preceding  test.  Dip  it  while  hot 
into  the  MnO2  and  heat  in  the  oxidizing  flame ;  if  only  a  little 
MnO2  is  used  the  bead  will  become  violet-red  when  cold.  It  can 
be  made  colorless  in  the  reducing  flame  by  steady  blowing.  If 

FIG.  289. 


more  is  used  the  bead  will  be  nearly  black  when  cold  before  reduc- 
tion and  amethystine  after  reduction. 

Or  cupric  oxide  or  oxide  of  nickel  may  be  dissolved  in  a  borax 
bead  until  the  bead  is  opaque,  and  then  reduced  on  charcoal  to  a 
clear  bead  and  a  metallic  button. 

*  When  the  flux  is  salt  of  phosphorus,  the  wire  should  be  held  over  the  flame  so  that 
the  ascending  hot  gases  will  help  to  retain  the  flux  upon  the  wire. 


CHAPTER   XII. 
OPERATIONS  OF  BLOWPIPE  ANALYSIS. 

Fusion.  The  degree  of  fusibility  and  manner  of  fusion  of  a  min- 
eral are  of  great  assistance  in  its  determination. 

The  degree  of  fusibility  is  stated  in  terms  of  a  scale  of  fusibility 
as  suggested  by  von  Kobell  or  sometimes  in  terms  such  as  easily 
fusible,  difficultly  fusible. 

The  scale  somewhat  modernized  is : 

Easily  Fusible. 

1.  Stibnite  or  Sulphur.     Fuse  in  closed  tube  below  red  heat 
Coarse  splinters  fuse  in  a  candle  or  gas  flame. 

2.  Chalcopyrite  or  Galenite.     Fuse  in  closed  tube  at  red  heat. 
Standard  splinters  fuse  in  luminous  flame. 

3.  Garnet  (Almandite)   or  Stilbite.     Standard  splinters    easily 
fuse  before  the  blowpipe  to  a  globule. 

4.  ActinoUU  or  Barite.     Standard  splinters  are  easily  rounded 
before  the  blowpipe.     Fine  splinters  fuse  easily  to  a  globule. 

Difficultly  Fusible 

5.  Orthoclase  or  Sphalerite.     Standard  splinter  rounded  on  thin 
edges    before    the    blowpipe.      Only    finest    splinters    fused    to    a 
globule. 

6.  Calamine  or  Enstatite.     Finest  edges  only  rounded  before 
blowpipe. 

Infusible. 

j.  Quartz  or  Topaz.  Retaining  edges  in  all  their  sharpness 
after  treatment. 

The  Test.  The  substance  should  be  tried  on  coal  to  see  if  vola- 
tile or  reducible.  If  not  then  as  shown  in  Fig.  290,  sharp  edged 
thin  splinters  of  some  approximately  constant  size  (say  1^x4  mm.) 
are  held  in  the  platinum  forceps  just  beyond  the  tip  of  the  blue 
flame. 

164 


OPERATIONS   OF  BLOWPIPE  ANALYSIS. 


I6S 


FIG.  290. 


If  easily  fused  or  reduced  on  coal,  the  platinum  forceps  must  be 
avoided  and  the  closed  tube  used  (for  I  and  2). 

If  in  powder,  or  with  a  tendency  to  crumble,  grind  and  mix 
with  water  to  fine  paste,  spread  thin  on  coal  and  dry,  and,  if  co- 
herent, hold  in  the  forceps. 

The  fragment  should  project 
beyond  the  platinum  as  in  Fig. 
290,  so  that  heat  may  not  be 
drawn. off  by  the  platinum,  and 
the  flame  directed  especially  upon 
the  point.  It  is  always  well  to 
examine  the  splinter  with  a  mag- 
nifying glass,  before  and  after 
heating. 

The  manner  of  fusion  may  be 
such  as  to  result  in  a  glass  or  slag  which  is  clear  and  transparent, 
or  white  and  opaque,  or  of  some  color,  or  filled  with  bubbles. 
There  may  be  a  frothing  or  intumescence,  or  a  swelling  and  split- 
ting (exfoliation).  In  certain  instances  the  color  and  form  may 
change  without  fusion,  etc. 

Flame  Coloration.  A  number  of  minerals  when  heated  color 
the  flame,  some  at  a  gentle  heat,  some  only  at  the  highest  heat 
attainable.  Repeated  dipping  of  the  mineral  in  hydrochloric  acid 
usually  assists  by  forming  volatile  chlorides.  A  good  method  to 
cover  all  cases  is  as  follows:  Arrange  a  black  background,  such 
as  a  piece  of  charcoal,  powder  the  substance  finely,  flatten  the  end 
of  a  clean  platinum  wire  and  dip  it  in  dilute  acid,  then  in  the 
powder,  and  hold  it  first  just  touching  the  flame  near  the  blowpipe 
and  then  at  the  tip  of  the  blue  flame. 

Merwin's  Color  Scale  *  consisting  of  three  colored  strips  of  celluloid  :  No.  I,  blue  ; 
No.  2,  overlapping  blue  and  violet ;  No.  3,  violet,  which  absorb  different  portions  of  the 
spectrum  is  most  satisfactory  for  distinguishing  the  red  flames  of  calcium,  strontium, 
lithium,  and  the  violet  flames  of  potassium  in  the  presence  of  sodium.  The  sodium 
coloration  is  absorbed  in  all  three,  the  observed  colors  for  the  rest  in  I,  2,  3  order  are 

Potassium Blue-violet  Violet  and  violet-red     Violet  and  violet-red 

Calcium Greenish  yellow     Absorbed  Faint  crimson 

Strontium  or  lithium Absorbed  Absorbed  Crimson 


*  Science,  Vol.  30,  p.  571. 


1 66  BLOWPIPE  ANALYSIS. 

The  important  flame  colorations  are  : 
Yellows. 

YELLOW.  — Sodium  and  all  its  salts.  Invisible  with  blue  glass. 
Reds. 

CARMINE.  —  Lithium  compounds.  Masked  by  soda  flame. 
Violet  through  blue  glass.  Invisible  through  green  glass. 

SCARLET.  —  Strontium  compounds.  Masked  by  barium  flame. 
Violet  red  through  blue  glass.  Yellowish  through  green  glass. 

YELLOWISH.  —  Calcium  compounds.  Masked  by  barium  flame. 
Greenish  gray  through  blue  glass.  Green  through  green  glass. 

Greens, 

YELLOWISH.  —  Barium  compounds,  molybdenum  sulphide  and 
oxide ;  borates  especially  with  sulphuric  acid  or  boracic  acid  flux. 
PURE  GREEN.  —  Compounds  of  tellurium  or  thallium. 
EMERALD.  —  Most  copper  compounds  without  hydrochloric  acid. 
BLUISH.  —  Phosphoric  acid  and  phosphates  with  sulphuric  acid. 
FEEBLE.  —  Antimony  compounds.     Ammonium  compounds. 
WHITISH.  —  Zinc. 

Blues. 

LIGHT. — Arsenic,  lead  and  selenium. 
AZURE.  —  Copper  chloride. 

WITH  GREEN,  —  Copper  bromide  and  other  copper  compounds 
with  hydrochloric  acid. 

Violet. 

Potassium  compounds.  Obscured  by  soda  flame.  Purple  red 
through  blue  glass.  Bluish  green  through  green  glass.  In  sili- 
cates improved  by  mixing  the  powdered  substance  with  an  equal 
volume  of  powdered  gypsum. 

USE  OF  THE  SPECTROSCOPE. 

When  salts  of  the  same  metal  are  volatilized  in  the  non-lumi- 
nous flame  of  a  Bunsen  burner  the  spectra  produced,  on  de- 
composing the  resultant  light  by  a  prism,  will  show  lines  identical 
in  color,  number  and  relative  position.  Salts  of  different  metals 
will  yield  different  lines. 

Although,  with  pure  salts,  the  already  described  flame  color- 
ations are  generally  distinct  and  conclusive,  it  will  frequently  hap- 
pen that  in  silicates  or  minerals  containing  two  or  more  reacting 


OPERATIONS   OF  BLOWPIPE  ANALYSIS. 


I67 


FIG.  291. 


substances  the  eye  alone  will  fail  to  identify  the  flame  coloration. 
It  is  well  therefore  to  supplement  the  ordinary  flame  tests  by 
spectroscopic  observation.  In  the  blowpipe  laboratory  the  chief 
use  of  the  spectroscope  will  be  to  identify  the  metals  of  the  potas- 
sium and  calcium  families  singly  or 
in  mixtures.  For  this  purpose  the 
direct  vision  spectroscope  of  Hoff- 
man, Fig  291,  is  the  most  con- 
venient. 

The  substance  under  examination 
should  be  moistened  with  hydro- 
chloric acid  and  brought  on  a  plati- 
num wire  into  the  non-luminous 
flame  of  the  Bunsen  burner  as  in  the 
ordinary  flame  test.  In  viewing  the 
flame  through  the  properly  adjusted 

spectroscope  certain  bright  lines  will  be  seen,  and  by  comparing 
these  with  the  chart,  Fig.  294,  or  with  substances  of  known  com- 
position, the  nature  of  the  substance  may  be  determined.  The 
sodium  line  will  almost  invariably  be  present  and  the  position  of 
the  other  lines  will  be  best  fixed  by  their  situation  relative  to  this 
bright  yellow  line. 

The  more  ordinary  form  of  spectroscope,  Fig.  292,  has  special 


FIG.  292. 


advantages  in  allowing  an  easy  comparison  of  flames.  A  is  the 
observation  telescope,  B  the  collimator  through  which  the  light 
from  the  flames  J/and  M'  is  sent  as  parallel  rays  through  the  prism 


i68 


BLOWPIPE  ANALYSIS. 


FIG.  293. 


collimator  and  its 
the  flame  G. 


P  to  the  telescope  A.  The  third  telescope 
C  sends  the  image  of  a  micrometer  scale  to 
A  by  which  the  relative  distance  apart  of 
the  lines  is  judged. 

Fig.  293  shows  an  enlarged  view  of  the 
collimator  B.     By  means  of  the  little  rect- 
angular prism  i  the  light  from  a  second  flame 
H,  placed  at  one   side,  is  sent  through  the 
spectrum  obtained  side  by  side  with  that  from 

FIG.  294. 


Ca 


•HHWWB 

Ted  org.  yellow 

The  chart  (Fig.  294)  and  brief  description  of  spectra  of  substances 
giving  distinct  lines  with  the  Bunsen  flame  will  be  of  service. 
POTASSIUM  —  two  red  lines  and  one  violet  line. 
SODIUM  —  a  single  bright  yellow  line,  which  with  higher  dispersion 

is  resolved  into  two   lines.      Almost  always  present  from 

the  small  amounts  of  sodium  in  dust. 
LITHIUM  —  one  very  bright  deep   red  line  and  a  faint  line  in  the 

orange. 

STRONTIUM  —  a  number  of  characteristic  red  lines  and  one  blue  line. 
CALCIUM  —  a  bright  red,  and  a  bright  green  line,  with  fainter  red 

to  yellow  lines  and  a  line  in  the  violet. 
BARIUM  —  a  number  of  yellow  and  green  lines. 


OPERATIONS    OF  BLOWPIPE  ANALYSIS.  169 

Absorption  Spectra. 

The  spectroscopic  examination  of  the  light  reflected  by  or  trans- 
mitted through  colored  minerals  is  likely  to  become  of  value  in 
their  identification. 

The  apparatus  used  may  be  a  separate  instrument  such  as  the 
"Pocket  Spectroscope"  with  absorption  spectrum  and  normal 
spectrum  side  by  side,  and  electrically  illuminated  wave-length 
scale  or  a  spectroscope  ocular  for  the  microscope,  and  it  must 
be  possible  to  determine  the  position  of  the  bands  with  accuracy. 

The  spectra  obtained  show  often  wide  somewhat  hazy  black 
bands  the  position  of  which  can  be  stated  between  limits  and  in 
other  instances  the  series  of  very  characteristic  sharp  bands  which 
some  can  be  closely  placed. 

In  certain  instances  the  bands  are  due  to  the  presence  of  known 
coloring  elements,  uranium,  the  rare  earths,  chromium,  vanadium, 
etc.  In  other  instances  the  elements  causing  the  colors  are  not 
known. 

In  certain  species  such  as  almandine  garnet  and  zircon  very  char- 
acteristic lines  are  obtained,  others  like  diamond  sometimes  give 
lines,  sometimes  do  not. 

VOLATILIZATION. 

In  blowpipe  analysis,  antimony,  arsenic,  cadmium,  zinc,  tin, 
lead,  mercury  and  bismuth  are  always  determined  by  securing 
sublimates  of  either  the  metals  themselves  or  of  some  volatile  oxide, 
iodide,  etc. 

Other  elements  and  compounds,  such  as  sulphur,  selenium,  tel- 
lurium, osmium,  molybdenum,  ammonia,  etc.,  are  also  volatilized 
and  in  part  determined  during  volatilization  as  odors  or  by  sub- 
limates. Certain  other  compounds,  particularly  chlorides  of  sodium 
and  potassium  and  of  some  other  metals,  such  as  copper,  tin  and 
lead,  yield  sublimates  ordinarily  disregarded. 

Volatilization  tests  are  commonly  obtained  on  charcoal,  or 
plaster  or  in  open  and  closed  tubes. 

Treatment  on  Charcoal. 

A  shallow  cavity,  just  sufficient  to  prevent  the  substance  slip- 
ping, is  bored  at  one  end  of  the  charcoal  and  a  small  fragment  or  a 
very  little  of  the  powdered  substance  is  placed  in  it.  The  charcoal 


I/O  BLOWPIPE  ANALYSIS. 

is  held  in  the  left  hand,  so  that  the  surface  is  at  right  angles  to  the 
lamp  but  tipped  vertically  at  about  120°  to  the  direction  in  which 
the  flame  is  blown. 

A  gentle  oxidizing  flame  is  blown,  the  blue  flame  not  touching 
the  substance,  but  being  just  behind  and  in  a  line  with  it.     After  a 

FIG.  295. 


few  moments  the  test  is  examined  and  all  changes  are  noted,  such 
as  position  and  color  of  sublimates,  color  changes,  odors,  decrepi- 
tation, deflagration,  formation  of  metal  globules  or  magnetic  parti- 
cles. The  heat  is  then  increased  and  continued  as  long  as  the 
same  reactions  occur,  but  if,  for  instance,  a  sublimate  of  new  color 
or  position  is  obtained,  it  is  often  well  to  remove  the  first  sublimate 
either  by  transferring  the  substance  to  another  piece  of  charcoal 
or  by  brushing  away  the  first  formed  sublimate  after  its  satisfac- 
tory identification. 

The  same  steps  should  then  be  followed  using  the  reducing 
flame. 

The  sublimates  differ  in  color  and  position  on  the  charcoal ;  some 
are  easily  removed  by  heating  with  the  oxidizing  flame,  some  by 
the  reducing  flame,  some  are  almost  non-volatile,  and  some  impart 
colors  to  the  flame. 

Treatment  on  Plaster  Tablets. 

Experience  has  shown  that  the  sublimates  obtained  on  charcoal 
and  plaster  supplement  each  other.  The  method  of  using  is  pre- 
cisely the  same  and  white  sublimates  are  easily  examined  by  first 
smoking  the  plaster  surface  by  holding  it  in  the  lamp  flame. 

The  coatings  differ  in  position,  and  to  some  extent  in  color. 


OPERATIONS  OF  BLOWPIPE   ANALYSIS.  17 1 

Plaster  is  the  better  conductor,  condenses  the  oxides  closer  to  the 
assay,  and  therefore,  the  more  volatile  coatings  are  thicker  and 
more  noticeable  on  plaster,  while  the  less  volatile  coatings  are  more 
noticeable  when  spread  out  on  charcoal.  Charcoal  supplements 
the  reducing  action  of  the  flame,  and  therefore  is  the  better  sup- 
port where  strong  reduction  is  desired. 


Comparison  of   Important  Sublimates  on  Charcoal    and    Plaster.* 

I.  Without  Fluxes.  —  Treated  First  in  0.  F.,  then  in  R.  F. 

ARSENIC. — White  volatile  coat.  On  smoked  plaster  it  is  crys- 
talline and  prominent ;  on  charcoal  it  is  fainter  and  less  distinct, 
but  the  odor  of  garlic  is  more  marked.  Deposits  at  some  distance 
from  assay.  Fumes  invisible  close  to  assay. 

ANTIMONY. — White  pulverulent  volatile  coat,  more  prominent 
on  charcoal.  Is  deposited  near  assay  and  the  fumes  are  visible 
close  to  assay  after  removal  of  flame. 

SELENIUM. 

On  Charcoal.  —  Horse-radish  odor  and  a  steel-gray  coat. 
On  Plaster.  —  Horse-radish  odor,  brick-red  to  crimson  coat. 

TELLURIUM. 

On  Charcoal. — White  coat  with  red  or  yellow  border. 
On  Plaster. — Deep  brown  coat. 
CADMIUM. 

On  Charcoal. — Brown  coat  surrounded  by  peacock  tarnish. 
On  Plaster. — Dark   brown  coat  shading  to  greenish-yellow 
and  again  to  dark  brown. 

MOLYBDENUM. — Crystalline  yellow  and  white  coat  with  an  outer 
circle  of  ultramarine  blue.  Most  satisfactory  on  plaster. 

LEAD. —       )  Yellow  sublimate  with  outer  fringe  of  white.   More 
BISMUTH. —  )      noticeable  on  charcoal  than  on  plaster. 
ZINC. — White,  not  easily  volatile  coat,  yellow  while   hot.     Best 
on  charcoal. 

TIN. — White  non-volatile  coat  close  to  assay,  yellowish  while 
hot.  Best  on  charcoal. 

*  Certain  compounds  give  a  white  coating  before  the  blowpipe  which  at  times  cause 
confusion.  Among  these  are  many  chlorides  and  'the  sulphate  of  lead.  Galena  and 
lead  sulphides  also  give  white  sublimates  which  must  not  be  confused  with  the  arsenic 
or  antimony  coats. 


BLOWPIPE  ANALYSIS. 

II.  With  Bismuth  Flux.* 
LEAD. 

On  Plaster. — Chrome  yellow  coat. 

On  Charcoal. — Greenish-yellow,  equally  voluminous  coat. 
BISMUTH. 

On  Plaster. — Chocolate-brown  coat,  with  an  underlying  scar- 
let; with  ammonia  it  becomes  orange-yellow,  and  later  cherry-red. 

On  Charcoal. — Bright  red  band  with  a  fringe  of  yellow. 
MERCURY. 

On  Plaster. — Scarlet  coat  with  yellow,  but  if  quickly  heated  is 
dull  yellow  and  black. 

On  Charcoal. — Faint  yellow  coat. 
ANTIMONY. 

On  Plaster. — Orange  coat  stippled  with  peach-red. 

On  Charcoal. — Faint  yellow  coat. 
ARSENIC. 

On  Plaster. — Yellow  and  orange  coat,  and  not  usually  satis- 
factory. 

On  Charcoal. — Faint  yellow  coat. 
TIN. 

On  Plaster. — Brownish-orange  coat. 

On  Charcoal. — White  coat. 
The  following  tests  show  only  on  the  plaster : 
SELENIUM. — Reddish-brown,  nearly  scarlet. 
TELLURIUM. — Purplish-brown  with  darker  border. 
MOLYBDENUM. — Deep  ultramarine  blue. 

III.  With  Soda  (Sodium  Carbonate  or  Bicarbonate). 
Soda  on  charcoal  exerts  a  reducing  action  partly  by  the  forma- 
tion of  sodium  cyanide,  partly  because  the  salts  sink  into  the  char- 
coal and  yield  gaseous  sodium  and  carbon  monoxide.     The  most 
satisfactory  method  is  to  mix  the  substance  with  three  parts  of  the 
moistened  reagent  and  a  little  borax ;  then  spread  on  the  char- 
coal and  treat  with  a  good  reducing  flame  until  everything  that 
can  be  absorbed  has  disappeared.    Moisten  the  charcoal  with  water, 
break  out  and  grind  the  portion  containing  the  charge.     Wash 
away  the  lighter  part  and  examine  the   residue  for  scales  and 
magnetic  particles. 

*  Two  parts  of  sulphur,  one  part  of  potassium  iodide,  one  part  of  acid  potassium 
sulphate. 


OPERATIONS   OF  BLOWPIPE  ANALYSIS.  1/3 

The  reduction  may  result  in : 

1 .  Coating,  but  no  reduced  metal. 

Volatile  white  coating  and  garlic  odor,  .  .  .  As. 
Reddish-brown  and  orange  coating  with  characteristic 

variegated  border, Cd. 

Non-volatile  coating,  yellow  hot  and  white  cold,  .         .  Zn. 

Volatile  steel-gray  coating  and  horseradish  odor,         .  Se. 

Volatile  white  coating  with  reddish  border,         .         .  Te. 

2.  Coating  with  reduced  metal. 

Volatile  thick  white  coating  and  gray  brittle  button,  .  Sb, 
Lemon-yellow  coating  and  reddish-white  brittle  button,  Bi. 
Sulphur-yellow  coating  and  gray  malleable  button,  .  Pb. 
Non-volatile  white  coating,  yellow  hot,  and  malleable 

white  button,  .  Sn. 

White  coating,  made  blue  by  touch  of  R.  R,  and  gray 

infusible  particles, Mo. 

3.  Reduced  metal  only \ 

Malleable  buttons, Cu,  Ag,  Au. 

Gray  magnetic  particles,  ....  Fe,  Co,  Ni. 
Gray  non-magnetic  infusible  particles,  W,  Pt,  Pd,  Ir,  Rh. 

The  carbonate  combines  with  many  substances  forming  both 
fusible  and  infusible  compounds.  Many  silicates  dissolve  with  a 
little  of  the  reagent,  but  with  more  are  infusible ;  a  few  elements 
form  colored  beads  with  the  reagent,  especially  on  platinum. 

The  residue  left  after  heating  may  contain  malleable  metallic 
beads  of  copper,  lead,  silver,  tin  or  gold.  It  may  consist  of  a 
brittle  easily  fusible  button  of  bismuth,  antimony,  or  the  sulphidef 
arsenide  or  antimonide  of  some  metal.  It  may  be  magnetic  from 
the  presence  of  iron,  cobalt  or  nickel  or  it  may  show  an  alkaline 
reaction,  when  touched  to  moistened  red  litmus  or  tumeric  paper, 
indicating  the  presence  of  some  member  of  the  potassium  or  cal- 
cium group  of  metals. 

Infusible  Compounds. — Mg,  Al,  Zr,  Th,  Y,  Gl. 

Fusible  Compounds. — SiO2  effervesces  and  forms  a  clear  bead  that 
remains  clear  on  cooling  if  the  reagent  is  not  in  excess. 

TiO2  effervesces  and  forms  a  clear  yellow  bead  crystalline  and 
opaque  on  cooling,- 

WO3  and  MoO3  effervesce  but  sink  in  the  charcoal. 

Ba,  Sr,  Ta,  V,  Nb  sink  into  the  charcoal. 

Ca  fuses,  then  decomposes,  and  the  soda  sinks  into  the  charcoal. 


1/4  BLOWPIPE  ANALYSIS. 

Colored  Beads.  —  Mn  forms  a  turquois  or  blue-green  opaque 
bead  with  soda  on  platinum  wire  in  the  oxidizing  flame. 

Cr  forms  a  chrome-yellow  opaque  bead  with  soda  on  platinum 
wire  in  the  oxidizing  flame,  which  becomes  green  in  reducing  flame. 

Sulphur  Reaction.  —  If  a  little  of  the  residue,  with  some  of  the 
charcoal  beneath,  is  taken  up  upon  the  point  of  a  knife  and  placed 
upon  a  wet  silver  coin,  the  coin  will  be  blackened  if  sulphur  was 
present  as  a  sulphide.  Sulphates  and  other  sulphur  compounds 
will  also  give  the  same  reaction  after  thorough  fusion.  The  test 
should  always  be  made  on  a  fresh  piece  of  charcoal. 
IV.  With  Metallic  Sodium. 

Reducing  effects  which  are  obtained  with  soda  only  by  hard 
blowing  may  be  accomplished  by  the  use  of  metallic  sodium  im- 
mediately and  with  the  greatest  ease.  The  metal  should  be 
handled  carefully  and  not  allowed  to  come  in  contact  with  water. 
It  should  be  kept  in  small  tightly  closed  bottles,  and  if  kept  cov- 
ered with  naphtha,  which  is  not  necessary,  care  should  be  taken 
that  the  naphtha  is  not  exposed  to  fire. 

A  cube  of  sodium  about  a  quarter-inch  in  diameter  is  cut  off 
with  a  knife  and  hammered  out  flat.  The  powdered  substance  is 
placed  upon  the  sodium,  pressed  into  it  and  the  whole  moulded 
into  a  little  ball  with  a  knife  blade.  This  sodium  ball  should  not 
be  touched  with  the  fingers,  for  if  some  oxides  are  present,  such  as 
lead  oxide,  spontaneous  combustion  may  take  place.  After  plac- 
ing the  sodium  ball  on  the  charcoal  it  should  be  touched  care- 
fully with  a  match  or  with  the  Bunsen  flame.  A  little  flash  ensues 
and  the  reduction  is  accomplished.  The  residue  can  now  be  safely 
heated  with  the  reducing  flame  of  the  blowpipe,  any  reduced  metal 
collected  together  and  the  sodium  compounds  volatilized  or  ab- 
sorbed by  the  charcoal.  When  present  in  sufficient  quantity,  beads 
of  the  malleable  metals  can  be  obtained  immediately  from  almost 
any  of  their  mineral  compounds  ;  metals,  like  zinc  and  tin,  which 
require  reduction  before  volatilization  yield  their  sublimates  with 
comparative  ease ;  and  if  a  little  of  the  charcoal  beneath  the  assay 
is  placed  on  a  wet  silver  coin  the  sulphur  reaction  will  be  obtained 
if  sulphur  was  present. 

In  general  the  results  are  the  same  as  outlined  for  soda  but  are 
much  more  easily  secured. 

Even  silica,  silicates,  borates,  etc.,  are  reduced  but  are  generally 
identified  by  other  means. 


OPERATIONS   OF  BLOWPIPE  ANALYSIS. 


175 


These  reactions  are  not  successful  on  plaster  tablets  on  account 
of  their  non-absorbent  character. 


inch  and  closed 
FIG.  296. 


Tests  in  Closed  Tubes. 

A  plain  narrow  glass  tube  about  4  inches  by 
at  one  end  is  best.     The  usual  purposes 
are  to  note   the  effects   of  heat  without 
oxidation,  and  to  effect  fusions  with  such 
reagents  as  KHSO4  or  KC1O3. 

Enough  of  the  substance  is  slid  down 
a  narrow  strip  of  paper,  previously  in- 
serted in  the  tube,  to  fill  it  to  the  height 
of  about  one  half  inch  ;  the  paper  is 
withdrawn  and  the  slightly  inclined  tube, 
Fig.  296,  heated  at  the  lower  end  grad- 
ually to  a  red  heat.  The  results  may 
be :  evolution  of  water,  odorous  and 
non-odorous  vapors,  sublimates  of  vari- 
ous colors,  decrepitation,  phosphores- 
cence, fusion,  charring,  change  of  color, 
and  magnetization. 
Acid  or  alkaline  moisture  in  the  upper 

part  of  tube, 

Odorless  gas   that  assists  combustion  (nitrates,  chlorates 
and  per  oxides),.         ....... 

Pungent  gas  that  whitens  lime  water,          . 

Odors. 

Odor  of  prussic  acid, 

Odor  of  putrid  eggs, 

Odor  that  suffocates,  fumes  colorless,  bleaching  action, 


H2O. 

O. 
CO2. 


Odor  that  suffocates,  fumes  violet,  .  .  .  .  I.* 

fumes  brown,  ....  Br. 

fumes  greenish  yellow,  .  .  Cl, 

fumes  etch  the  glass,  .  .  F. 

Odor  of  nitric  peroxide,  fumes  reddish-brown,          .  NO2. 

Odor  of  ammonia,  fumes  colorless  or  white,    .          .  NH3.f 


CN. 
H2S. 
SO2. 


*I,   Br,   Cl,   F  and  N2O5  are  assisted  by   mixing  substance  with  acid  potassium 
sulphate.  f  NH3,  Hg,  As,  Cd  are  assisted  by  mixing  with  soda. 


BLOWPIPE  ANALYSIS. 


Sublimates. 

Sublimate  white,  fusing  yellow,        ....  PbCl2. 

fusing  to  drops,  disagreeable  odor,  Os. 

and  volatile, NH4  (salts). 

yellow  hot,  infusible,      .         .         .  HgCl. 

yellow  hot,  fusible,         .         .         .  HgCl2. 

fusible,  needle  crystals,  .         .  Sb2O3. 

volatile,  octahedral  crystals,  .         .  As2O3. 

fusible,  amorphous  powder,   .         .  TeO2. 

Sublimate  mirror-like,  collects  in  globules,       .         .  Hg. 

does  not  collect  in  globules,  .  As,  Cd,  Te. 

Sublimate  red  when  hot,  yellow  cold,       .         .         .  S. 

Sublimate  dark  red  when  hot,  reddish-yellow  cold,  .  As2S3. 

Sublimate  black  when  hot,  reddish-brown  cold,         .  Sb2S3. 

Sublimate  black,  but  becomes  red  when  rubbed,       .  HgS. 
Sublimate   red   to   black,  but   becomes    red    when 

rubbed, Se. 

Color  of  substances  changes 

from  white  to  yellow,  cools  yellow,  .         .         .  PbO. 

from  white  to  yellow,  cools  white,     .         .         .  ZnO. 

from  white  to  dark  yellow^  cools  light  yellow, .  Bi2O3. 

from  white  to  brown,  cools  yellow,  .         .         .  SnO2. 

from  white  to  brown,  cools  brown,   .         .         .  CdO. 
from  yellow  or  red  to  darker,  after  strong  heat, 

cools  green, Cr2O3. 

from  red  to  black,  cools  red,.    ....  Fe2O8. 

from  blue  or  green  to  black,  cools  black,  .  CuO. 

Tests  in  Open  Glass  Tubes. 

By  using  a  somewhat  longer 
tube,  open  at  both  ends  and 
held  in  an  inclined  position,  a 
current  of  air  is  made  to  pass 
over  the  heated  substance,  and 
thus  many  substances  not  vola- 
tile in  themselves  absorb  oxy- 
gen and  release  volatile  oxides. 
The  substance  should  be  in 
state  of  powder. 

Place  the  assay  near  the  lower 


OPERATIONS    OF  BLOWPIPE  ANALYSIS. 


177 


end  of  the  tube,  Fig.  297,  and  heat  gently, 

creasing   the    air  current  by  holding    the 

nearly  vertical. 

Odor  that  suffocates,  bleaching  action, 

Odor  of  rotten  horseradish, 

Odor  of  garlic, .         .         . 

Sublimate  white  volatile  octahedral  crystals, 

Sublimate  white  partially  volatile,  fusible 
to  yellow  drops,  pearl  gray  cold, 

Sublimate  white  non-volatile  powder,  dense 
fumes, 

Sublimate  white  non-volatile  powder,  fu- 
sible to  colorless  drops, 

Sublimate  white  non-volatile  powder,  fusi- 
ble to  yellow  drops,  white  when  cold, 

Sublimate  white  non-volatile  fusible 
powder, 

Sublimate  gray,  red  at  distance, 

Sublimate  yellow  hot,  white  cold,  crystal- 
line near  the  assay,  blue  in  reducing 
flame, 

Sublimate  brown  hot,  yellow  cold,  fusible, 

Sublimate  metallic  mirror, 


and  then  strongly,  in- 
tube    more    and  more 

SO2,  indicating  S. 
Se02,         ' 
As203,       ' 

As203,       < 

PbOCl,      ' 

Sb2o3,     • 

Te02,        " 
PbS04,      « 

BiS04,      " 
Se02, 


Se. 
As. 
As. 

PbCl,. 
Sb. 
Te. 
PbS. 

BiS. 
Se. 


Mo03, 
Bi203, 


Mo. 

Bi. 

Hg. 


Bead  Tests  with  Borax  and  with  Salt  of  Phosphorus. 

Preliminary  to  bead  tests,  many  compounds,  sulphides,  arsenides, 
arsenates,  etc.,  may  be  converted  into  oxides  by  roasting  as  follows  : 

Treat  in  a  shallow  cavity  on  charcoal  at  a  dull  red  heat,  never 
allowing  the  substance  to  fuse  or  even  sinter.  Use  a  feeble  oxidiz- 
ing flame  to  drive  off  sulphur,  then  a  feeble  reducing  flame  to 
reduce  arsenical  compounds,  then  reheat  in  an  oxidizing  flame. 
Turn,  crush,  and  reroast  until  no  sulphurous  or  garlic  odor  is 
noticeable. 

Sodium  tetraborate  or  borax  may  be  considered  as  made  up  of 
sodium  metaborate  and  boron  trioxide.  The  boron  trioxide  at  a 
high  temperature  combines  with  metallic  oxides,  driving  out  volatile 
acids,  and  by  the  aid  of  the  oxidizing  flame  the  resulting  borates 
fuse  with  the  sodium  metaborate  to  form  double  borates  which  are 
often  of  a  characteristic  color.  The  color  may  differ  when  hot  and 
cold  and  according  to  the  degree  of  oxidation  and  reduction. 
13 


178  BLOWPIPE  ANALYSIS. 

Sodium  ammonium  phosphate,  or  salt  of  phosphorus,  by  fusion 
loses  water  and  ammonia  and  becomes  sodium  metaphosphate. 
The  sodium  metaphosphate  at  high  temperatures  combines  with 
metallic  oxides  to  form  double  phosphates  and  pyrophosphates, 
which  like  the  double  borates  are  frequently  colored,  although  the 
colors  often  differ  from  those  obtained  with  borax. 

A  bead  of  either  flux  is  made  on  platinum  wire  as  described  on 
page  162,  and  the  substance  is  added  gradually  to  the  warm  bead 
and  fused  with  it  in  the  oxidizing  flame.  The  ease  of  dissolving, 
effervescence,  color,  change  of  color,  etc.,  should  be  noted. 

We  may  greatly  simplify  the  tabulation  of  results  by  the  follow- 
ing division : 

1.  Oxides  which  Color  neither  Borax  or  Salt  of  Phosphorus,  or  at 

Most  Impart  a  Pale  Yellow  to  the  Hot  Bead  when  Added 
in  Large  Amounts. 

OXIDES  OF  NOTICEABLE  DISTINCTIONS. 

ALUMINUM.  — Cannot  be  flamed  opaque. 
ANTIMONY.  — Yellow  hot  in  oxidizing  flame,  flamed    opaque 

gray  in  reducing  flame,  on  charcoal  with  tin 

black.     Expelled  by  reducing  flame  in  time. 
BARIUM.       — Flamed  opaque  white. 
BISMUTH.     — Like  antimony. 
CADMIUM.    — Like  antimony,  but  not  made   black  by  fusion 

with  tin. 

CALCIUM.     — Like  barium. 
LEAD.  — Like  antimony,  but  not   made  black    by  fusion 

with  tin. 

MAGNESIUM. — Like  barium. 

SILICON.       — Only  partially  dissolved  in  salt  of  phosphorus. 
STRONTIUM.  — Like  barium. 
TIN.  — Like  aluminum. 

ZINC.  — Like    antimony,   but  not  made   black  by  fusion 

with  tin. 

I 

2.  Oxides  which  Impart  Decided  Colors  to  the  Beads. 

The  colors  in  hot  and  cold  beads  of  both  fluxes  and  under  both 
oxidation  and  reduction  are  shown  in  the  following  table.  The 
abbreviations  are  :  sat  =  saturated  ;  fl  =  flamed  ;  op  =  opaque. 


OPERATIONS   OF  BLOWPIPE  ANALYSIS. 


179 


Hot  and  cold  relate  to  same  bead  ;  hot  and  cold  to  larger  amounts 
of  the  oxide. 


OXIDES  OF 

VIOLET. 

BLUE. 

GREEN. 

RED. 

BROWN. 

YELLOW. 

COL'L'SS 

Chromium, 

O.F. 
R.F 

cold 
hot,  cold 

hot 

hot 

Cobalt, 

O.F. 
R.F. 

hot,  cold 
hot,  cold 

Copper, 

O.F. 
R.F. 

cold 

hot 

cold  (op.) 

cold 

hot 

Iron, 

O.F. 
R.F. 

hot,  cold 

hot 

hot,  cold 

cold 

c 
<J 
w 

Manganese, 

O.F. 
R.F. 

hot  cold 

cold 

hot,  cold 

X 
<! 

p/ 

Molybdenum, 

O.F 
R.F. 

hot  (sat.) 

hot,  cold 

hot 

cold 

g 

Nickel, 

O.F. 
R.F. 

hot 

cold 

hot,  cold 

Titanium, 

O.F 
R.F. 

flamed 

hot,  cold 

hot 
hot,  cold 

hot,  cold 

Tungsten, 

O.F. 
R.F. 

cold 

Aojf  (sat.) 
hot 

hot,  cold 
cold 

Uranium, 

O.F. 
R.F. 

hot,  cold 

hot 

hot,cold(fl.) 

Vanadium, 

O.F. 
R.F. 

cold 

hot 

hot,  cold 

hot,  cold 

OXIDES  OF 

VIOLET. 

BLUB. 

GREEN. 

RED. 

BROWN. 

YELLOW. 

COL'L'SS 

Chromium, 

O.F. 
R.F. 

cold 
cold 

hot 

hot 

Cobalt, 

O.F. 
R.F. 

hot,  cold 
hot,  cold 

t 

<? 

Copper, 

O.F. 
R.F. 

cold 
hot 

hot 

cold  (op  ) 

m 

K 
CO 

Iron, 

O.F. 
R.F. 

hot 
hot,  cold 

cold 
cold 

hot,  cold 
hot 

cold 
cold 

u 
& 

0 

V 

Manganese, 

O.F. 
R.F. 

hot,  cold 

hot,  cold 

K 

8 

rr 

Molybdenum, 

O.F. 
R.F. 

hot 
hot,  cold 

cold 

PH 

c 

Nickel, 

O.F. 
R.F. 

hot 
hot 

cold 

cold 

H 

_) 
4 

Titanium, 

O.F. 
R.F. 

cold 

hot 
hot 

hot,  cold 

Tungsten, 

O.F. 
R.F. 

cold 

hot 

hot  (sat.) 

hot,  cold 

Uranium, 

O.F. 
R.F. 

cold 
hot,  cold 

hot 

Vanadium, 

O.F. 
R.F. 

cold 

hot 

hot,  cold 

180  BLOWPIPE  ANALYSIS. 

FLAMING. 

Some  substances  yield  a  clear  glass  with  borax  or  salt  of  phos- 
phorus, which  remains  clear  when  cold,  but  at  a  certain  point  near 
saturation  if  heated  slowly  and  gently  or  with  an  intermittent  flame, 
or  unequally,  or  by  alternate  oxidizing  flame  and  reducing  flame, 
the  bead  becomes  opaque  and  enamel-like. 

Testing  Solubility. 

Solubility  in  Water. — Ordinarily  the  absence  of  a  taste  or  of 
some  evidence  of  exposure  such  as  a  dull  surface  or  damp  condi- 
tion or  tendency  to  fall  to  powder  or  even  a  hardness  above  3 
prove  insolubility  in  water. 

But  as  recognition  of  the  kind  of  taste  is  not  usually  easy  it  is 
better  to  heat  the  powdered  substance  with  water  and  allow 
several  drops  of  the  solution  to  evaporate  on  a  glass  slip,  usually 
obtaining  a  very  characteristic  recrystallization  either  of  the  orig- 
inal substance  or  crystals  of  some  new  compound. 

Solubility  in  Dilute  Hydrochloric  Acid. — Dilute  (i :  i)  hydro- 
chloric acid  is  generally  used  to  determine  the  ease  or  degree  of 
solubility.  This  test  fails  only  from  carelessness.  The  substance 
must  be  selected  as  nearly  pure  as  possible,  finely  ground  and 
added  to  the  acid  in  successive  small  quantities.  A  clear  solution 
should  be  aimed  at,  acid  being  added  if  more  is  needed  until 
everything  has  dissolved.  If  complete  solution  cannot  be 
obtained,  the  liquid  must  be  filtered  and  the  clear  filtrate 
slowly  and  partially  evaporated  until  separation  commences. 
If  doubt  exists  as  to  solubility  the  liquid  must  be  evaporated  to 
dryness,  a  residue  proving  solution  to  have  taken  place. 

During  the  treatment  carbonates  and  some  sulphides  are 
decomposed  and  CO2  or  H2S  escapes  with  effervescence.  The 
odor  of  H2S  is  easily  recognized.  Some  silicates  will  yield  on 
partial  evaporation  a  cake  of  jelly,  others  lumps  of  jelly,  others 
fine  pulverulent  silica.  Still  other  minerals  may  form  character- 
istic crystals  or  residues. 

Effect  of  Concentrated  Hydrochloric  Acid. — With  a  glass  rod 
place  a  single  drop  of  acid  on  a  smooth  surface  of  the  mineral  (or 
upon  an  object  glass,  adding  a  few  particles  of  the  powdered 
mineral).  Let  this  acid  nearly  dry,  and  examine  under  the 
microscope. 


OPERATIONS   OF  BLOWPIPE  ANALYSIS.  l8l 

Effect  of  Dilute  Hydrofluoric  Acid. — Some  minerals  unaffected 
by  other  acids  are  dissolved  by  this.  Dip  the  stone  in  melted 
paraffine  and  mark  a  cross  or  other  convenient  shape  through  the 
paraffine  above  some  unimportant  face.  Immerse  for  y2  hour  in 
the  acid  (i  c.p.  acid  and  2  water),  remove,  wash,  and  clean  off  the 
paraffine.  If  the  cross  shows,  then  the  mineral  is  soluble. 

Tests  with  Cobalt  Solution. 

Cobalt  nitrate  dissolved  in  ten  parts  of  water  is  used  to  moisten 
light  colored  infusible  substances.  These  are  then  strongly  heated 
on  charcoal  in  the  oxidizing  flame  and  colored  compounds  result. 

BLUE,  A12O3  and  minerals  containing  it.     Silicates  of  zinc. 

GREEN  (bluish),  SnO2. 

GREEN  (yellowish),  ZnO,  TiO2. 

GREEN  (dark),  oxides  of  antimony  and  columbium. 

FLESH  COLOR,  MgO,  and  minerals  containing  it. 

Certain  other  substances  yield  colors  if  strongly  heated,  cooled, 
and  then  moistened  with  the  cobalt  solution  without  reheating. 
Certain  minerals  boiled  with  cobalt  solution  are  colored  thereby. 


CHAPTER   XIII. 
SUMMARY   OF   USEFUL   TESTS   WITH   THE   BLOWPIPE. 

THE  details  of  ordinary  manipulations,  such  as  obtaining  beads, 
flames,  coatings  and  sublimates,  are  omitted  and  the  results  alone 
stated;  unusual  manipulations  are  described.  The  bead  tests 
are  supposed  to  be  obtained  with  oxides ;  the  other  tests  are  true, 
in  general,  of  all  compounds  not  expressly  excluded.  The  course 
to  be  followed  in  the  case  of  interfering  elements  is  briefly  stated. 

ALUMINUM,  Al. 

With  Soda. — Swells  and  forms  an  infusible  compound. 
With  Borax  or  S.  Ph. — Clear  or  cloudy,  never  opaque. 
With  Cobalt  Solution* — Fine  blue  when  cold. 

AMMONIUM,  NH4. 

In  Closed  Tube. — Evolution  of  gas  with  the  characteristic  odor. 
Soda  or  lime  assists  the  reaction.  The  gas  turns  red  litmus  paper 
blue  and  forms  white  clouds  with  HC1  vapor. 

ANTIMONY,  Sb. 

On  Coal,  R.  F."\ — Volatile  white  coat,  bluish  in  thin  layers,  con- 
tinues to  form  after  cessation  of  blast  and  appears  to  come  directly 
off  the  mass. 

With  Bismuth  Flux: 

On  Plaster. — Peach-red  coat,  somewhat  mottled. 
On  Coal. — Faint  yellow  or  red  coat. 


*  Certain  phosphates,  berates  and  fusible  silicates   become   blue  in  absence   of 
alumina. 

•{-  This  coat  may  be  further  tested  by  S .  Ph.  or  flame. 

182 


USEFUL    TESTS    WITH  THE  BLOWPIPE.  1^3 

In  Open  Tube. — Dense,  white,  non-volatile,  amorphous  sublimate. 
The  sulphide,  too  rapidly  heated,  will  yield  spots  of  red. 

In  Closed  Tube. — The  oxide  will  yield  a  white  fusible  sublimate 
of  needle  crystals,  the  sulphide,  a  black  sublimate  red  when  cold. 

Flame. — Pale  yellow- green. 

With  S.  Ph. — Dissolved  by  O.  F.  and  fused  on  coal  with  tin  in 
R.  F.  becomes  gray  to  black. 

INTERFERING  ELEMENTS. 

Arsenic. — Remove  by  gentle  O.  F.  on  coal. 

Arsenic  with  Sulphur. — Remove  by  gentle  heating  in  closed 
tube. 

Copper. — The  S.  Ph.  bead  with  tin  in  R.  F.  may  be  momentarily 
red  but  will  blacken. 

Lead  or  Bismuth. — Retard  formation  of  their  coats  by  inter- 
mittent blast,  or  by  adding  boracic  acid.  Confirm  coat  by  flame, 
not  by  S.  Ph. 

ARSENIC,  As. 

On  Smoked  Plaster. — White  coat  of  octahedral  crystals. 

On  Coal. — Very  volatile  white  coat  and  strong  garlic  odor. 
The  oxide  and  sulphide  should  be  mixed  with  soda. 

With  Bismuth  Flux: 

On  Plaster. — Reddish  orange  coat. 
On  Coal. — Faint  yellow  coat. 

In  Open  Tube. — White  sublimate  of  octahedral  crystals.  Too 
high  heat  may  form  deposit  of  red  or  yellow  sulphide. 

In  Closed  Tube. — May  obtain  white  oxide,  yellow  or  red  sul- 
phide, or  black  mirror  of  metal.  If  the  tube  is  broken  and  the 
mirror  heated,  a  strong  garlic  odor  will  be  noticed. 

Flame. —  Pale  azure  blue. 

INTERFERING  ELEMENTS. 

Antimony. — Heat  in  closed  tube  with  soda  and  charcoal,  break 
and  treat  resulting  mirror  in  O.  F.  for  odor. 

Cobalt  or  Nickel.  —  Fuse  in  O.  F.  with  lead  and  recognize  by 
odor. 

Sulphur. — (a)  Red  to  yellow  sublimate  of  sulphide  of  arsenic  in 

closed  tube. 
(b)  Odor  when  fused  with  soda  on  charcoal. 


1 84  BLOWPIPE  ANALYSIS. 

BARIUM,  Ba. 

On  Coal  with  Soda. — Fuses  and  sinks  into  the  coal. 
Flame. — Yellowish  green  improved  by  moistening  with  HCi. 
With  Borax  or  S.   Ph. — Clear   and  colorless,  can   be  flamed 
opaque-white. 

BISMUTH,  Bi. 

On  Coal. — In  either  flame  is  reduced  to  brittle  metal  and  yields 
a  volatile  coat,  dark  orange  yellow  hot,  lemon  yellow  cold,  with 
yellowish-white  border. 
With  Bismuth  Flux:* 

On  Plaster. — Bright  scarlet  coat  surrounded  by  chocolate 
brown,  with  sometimes  a  reddish  border.     The  brown 
may  be  made  red  by  ammonia.f 
On  Coal. — Bright  red  coat  with  sometimes  an  inner  fringe 

of  yellow. 

With  S.  Ph. — Dissolved  by  O.  F.  and  treated  on  coal  with 
tin  in  R.  F.  is  colorless  hot  but  blackish  gray  and  opaque 
cold. 

INTERFERING  ELEMENTS. 

Antimony. — Treat  on  coal  with  boracic  acid,  and  treat  the  re- 
sulting slag  on  plaster  with  bismuth  flux. 
Lead. — Dissolve  coat  in  S.  Ph.  as  above. 

BORON,  B. 

All  borates  intumesce  and  fuse  to  a  bead. 

Flame. — Yellowish  green.  May  be  assisted  by  :  (a]  Moistening 
with  H2SO4;  ($)  Mixing  to  paste  with  water,  and  boracic  acid 
flux  (4j£  pts.  KHSO4,  I  pt.  CaF2) ;  (c)  By  mixing  to  paste  with 
H3SO4  and  NH4F. 

BROMINE,  Br. 

With  S.  Ph.  Saturated  With  CuO.— Treated  at  tip  of  blue  flame, 
the  bead  will  be  surrounded  by  green  and  blue  flames. 
In  Matrass  With  KHSO^. — Brown  choking  vapor. 

INTERFERING  ELEMENTS. 

Silver. — The  bromide  melts  in  KHSO4  and  forms  a  blood-red 
globule  which  cools  yellow  and  becomes  green  in  the  sunlight. 

*  Sulphur  2  parts,  potassic  iodide  I  part,  potassic  bisulphate  I  part, 
f  May  be  obtained  by  heating  S.  Ph.  on  the  assay. 


USEFUL    TESTS    WITH  THE  BLOWPIPE.  185 

CADMIUM,  Cd. 

On  CoalR.  F. — Dark  brown  coat,  greenish  yellow  in  thin  layers. 
Beyond  the  coat,  at  first  part  of  operation,  the  coal  shows  a  varie- 
gated tarnish. 

On  Smoked  Plaster  with  Bismuth  Flux. — White  coat  made  orange 
by  (NH4)2S. 

With  Borax  or  S.  Ph. — O.  F.  clear  yellow  hot,  colorless  cold, 
can  be  flamed  milk-white.     The  hot  bead  touched  to 
Na2S2O3  becomes  yellow. 

R.  F.  Becomes  slowly  colorless. 

INTERFERING  ELEMENTS. 

Lead,  Bismuth,  Zinc. — Collect  the  coat,  mix  with  charcoal  dust 
and  heat  gently  in  a  closed  tube.  Cadmium  will  yield  either  a 
reddish  brown  ring  or  a  metallic  mirror.  Before  collecting  coat 
treat  it  with  O.  F.  to  remove  arsenic. 

CALCIUM,  Ca. 

On  Coal  with  Soda. — Insoluble  and  not  absorbed  by  the  coal. 
Flame. — Yellowish  red  improved  by  moistening  with  HC1. 
With  Borax  or  S.  Ph. — Clear  and  colorless,  can  be  flamed  opaque. 

CARBON  DIOXIDE,  C02. 

With  Nitric  Acid.— Heat  with  water  and  then  with  dilute  acid. 
CO.,  will  be  set  free  with  effervescence.  The  escaping  gas  will 
render  lime-water  turbid. 

With  Borax  or  S.  Ph. — After  the  flux  has  been  fused  to  a  clear 
bead,  the  addition  of  a  carbonate  will  cause  effervescence  during 
further  fusion. 

CHLORINE,  Cl. 

With  S.  Ph.  Saturated  with  CuO.— Treated  at  tip  of  blue  flame, 
the  bead  will  be  surrounded  by  an  intense  azure-blue  flame. 

On  Coal  with  CuO. — Grind  with  a  drop  of  H2SO4,  spread  the 
paste  on  coal,  dry  gently  in  O.  F.  and  treat  with  blue  flame,  which 
will  be  colored  greenish-blue  and  then  azure-blue. 

CHROMIUM,  Cr. 

With  Borax  or  S.  Ph. — O.  F.  Reddish  hot,  fine  yellow-green 
cold. 


1 86  BLOWPIPE  ANALYSIS. 

R.  F.  In  borax,  green   hot  and  cold.     In  S.  Ph.  red  hot, 

green  cold. 
With  Soda. — O.  F.  Dark  yellow  hot,  opaque  and  light  yellow 

cold.      R.  F.  Opaque  and  yellowish-green  cold. 
In  tube  with  KHSO^.  —  Dark  violet  hot,  greenish  cold. 

INTERFERING  ELEMENTS. 

Manganese.— The  soda  bead  in  O.  F.  will  be  bright  yellowish- 
green. 

COBALT,  Co. 

On  Coal,  R.  F. — The  oxide  becomes  magnetic  metal.     The  solu- 
tion in  HC1  will  be  rose-red  but  on  evaporation  will  be  blue. 
With  Borax  or  S.  Ph. — Pure  blue  in  either  flame. 

INTERFERING  ELEMENTS. 

Arsenic ,  Sulphur,  or  Selenium. — Roast  and  scorify  with  succes- 
sive additions  of  borax.  If  other  elements  are  present  which  color 
strongly  the  glasses  will  be  in  order  given  :  Yellow  (iron),  green 
(iron  and  cobalt),  blue  (cobalt),  reddish-brown  (nickel),  green 
(nickel  and  copper),  blue  (copper).  Metallic  lead  or  gold  may  be 
used  to  collect  the  metals  as  described,  p.  201. 

COLUMBIUM,  Cb. 

Heat  strongly  on  coal  with  borax,  crush  and  dissolve  in  cone. 
HC1  and  add  metallic  tin.  A  bluish-gray  color,  disappearing  on 
moderate  dilution  indicates  Cb.  Tungsten  under  same  conditions 
remains  blue. 

COPPER,  Cu. 

On  Coal  R.  F. — Formation  of  red  malleable  metal. 

F/ame* — Emerald-green  or  azure-blue,  according  to  compound. 

The  azure-blue  flame  may  be  obtained : 

(a)  By  moistening  with  HC1  or  aqua  regia,  drying  gently  in  O. 
F.  and  heating  strongly  in  R.  F. 

(b)  By  saturating  S.  Ph.  bead  with   substance,  adding  common 
salt,  and  treating  with  blue  flame. 

With  Borax  \  or  S.  Ph. — O.  F.  Green  hot,  blue  or  greenish- 
blue  cold. 

*  Sulphur,  selenium  and  arsenic  should  be  removed  by  roasting.    Lead  necessitates 
a  gentle  heat. 

f  By  repeated  slow  oxidation  and  reduction,  a  borax  bead  becomes  ruby  red. 


USEFUL    TESTS    WITH  THE  BLOWPIPE.  l8/ 

R.  F.  Greenish  or  colorless  hot,  opaque  and  brownish-red 
cold.     With  tin  on  coal  this  reaction  is  more  delicate. 

INTERFERING  ELEMENTS. 

General  Method* — Roast  thoroughly,  treat  with  borax  on  coal 
in  strong  R.  F.,  and 

If  Button  Forms. — Separate  the  button  from  the  slag,  remove 
any  lead  from  it  by  O.  F.,  and  make  either  S.  Ph.  or  flame 
test  upon  residual  button. 

If  no  Visible  Button  Forms. — Add  test  lead  to  the  borax  fusion, 
continue  the  reduction,  separate  the  button  and  treat  as  in 
next  test.  (Lead  Alloy.) 

Lead  or  Bismuth  Alloys. — Treat  with  frequently  changed  boracic 
acid  in  strong  R.  F.,  noting  the  appearance  of  slag  and  residual 
button. 

Trace. — A  red  spot  in  the  slag. 

Over  One  Per  Cent. — The  residual  button  will  be  bluish-green 
when  melted,  will  dissolve  in  the  slag  and  color  it  red  upon 
application  of  the  O.  F.,  or  may  be  removed  from  the  slag 
and  be  submitted  to  either  the  S.  Ph.  or  the  flame  test. 

FLUORINE,  F. 

Etching  Test. — If  fluorine  is  released  it  will  corrode  glass  in 
cloudy  patches,  and  in  presence  of  silica  there  will  be  a  deposit 
on  the  glass.  According  to  the  refractoriness  of  the  compound 
the  fluorine  may  be  released  : 

(a)  In  closed  tube  by  heat. 

(b)  In  closed  tube  by  heat  and  KHSO4 

(c)  In  open  tube  by  heat  and  glass  of  S.  Ph. 

With  Cone.  H^SO^  and  SiO2. — If  heated  and  the  fumes  condensed 
by  a  drop  of  water  upon  a  platinum  wire,  a  film  of  silicic  acid  will 
form  upon  the  water. 

IODINE,  I. 

With  S.  Ph.  Saturated  with  CuO. — Treated  at  the  tip  of  the  blue 
flame  the  bead  is  surrounded  by  an  intense  emerald-green  flame. 

In  Matrass  with  KHSO±. — Violet  choking  vapor  and  brown 
sublimate. 

*  Oxides,  sulphides,  sulphates  are  best  reduced  by  a  mixture  of  soda  and  borax. 


1 88  BLOWPIPE  ANALYSIS. 

In  Open   Tube  with  Equal  Parts  Bismuth  Oxide,  Sulphur  and 
Soda. — A  brick-red  sublimate. 

With  Starch  Paper. — The  vapor  turns  the  paper  dark  purple. 

INTERFERING  ELEMENTS. 

Silver. — The  iodide  melts  in  KHSO4  to  a  dark  red  globule,  yel- 
low on  cooling,  and  unchanged  by  sunlight. 

IRON,  Fe. 

On   Coal. — R.  F.  Many  compounds  become  magnetic.     Soda 
assists  the  reaction. 

With  Borax* — O.  F.  Yellow  to  red  hot,  colorless  to  yellow  cold. 

R.  F.  Bottle-green.     With  tin  on  coal,  vitriol-green. 
With  S.  Ph. — O.  F.  Yellow  to  red  hot,  greenish  while  cooling, 

colorless  to  yellow  cold. 

R.  F.  Red  hot  and  cold,  greenish  while  cooling. 
State  of  the  Iron* — A  borax  bead  blue  from  CuO  is  made  red  by 
FeO,  and  greenish  by  Fe2O3. 

INTERFERING  ELEMENTS. 

Chromium. — Fuse  with  nitrate  and  carbonate  of  soda  on  pla- 
tinum, dissolve  in  water  and  test  residue  for  iron. 

Cobalt. — By  dilution  the  blue  of  cobalt  in  borax  may  often  be 
lost  before  the  yellow  of  iron. 

Copper. — May  be  removed  from  borax  bead  by  fusion  with  lead 
on  coal  in  R.  F. 

Manganese. — (a)  May  be  faded  from  borax  bead  by  treatment 

with  tin  on  coal  in  R.  F. 
(b)  May  be  faded  from  S.  Ph.  bead  by  R.  F. 

Nickel. — May  be  faded  from  borax  bead  by  R.  F. 

Tungsten  or  Titanium. — The  S.  Ph.  bead  in  R.  F.  will  be  reddish- 
brown  instead  of  blue  or  violet. 

Uranium. — As  with  chromium. 

Alloys,  Sulphides,  Arsenides,  etc. — Roast,  treat  with  borax  on  coal 
in  R.  F.,  then  treat  borax  in  R.  F.  to  remove  reducible  metals. 

LEAD,  Pb. 

On  Coal.\—\K  either  flame  is   reduced  to  malleable  metal  and1 

*  A  slight  yellow  color  can  only  be  attributed  to  iron,  when  there  is  no  decided  color 
produced  by  either  flame  in  highly  charged  beads  of  borax  and  S.  Ph. 
f  The  phosphate  yields  no  coat  without  the  aid  of  a  flux. 


USEFUL    TESTS    WITH   THE  BLOWPIPE.  189 

yields,  near  the  assay,  a  dark  lemon-yellow  coat,  sulphur-yellow 
cold  and  bluish- white  at  border. 
With  Bismuth  Flux: 

On  Plaster. — Chrome-yellow  coat,  blackened  by  (NH4)2S. 
On  Coal. — Volatile  yellow  coat,  darker  hot. 
Flame. — Azure-blue. 

With  Nitric  Acid  and  Potassic  Iodide. — Place  a  drop  of  i-i 
HNO3  on  the  sample.  On  this  drop  sprinkle  a  little  powdered 
KI.  "  If  Pb  is  present  a  vivid  yellow  color  soon  appears." 

INTERFERING  ELEMENTS. 

Antimony. — Treat  on  coal  with  boracic  acid,  and  treat  the  re- 
sulting slag  on  plaster  with  bismuth  flux. 

Arsenic  Sulphide. — Remove  by  gentle  O.  F. 

Cadmium. — Remove  by  R.  F. 

Bismuth. — Usually  the  bismuth  flux  tests  on  plaster  are  sufficient 
In  addition  the  lead  coat  should  color  the  R.  F.  blue. 

LITHIUM,  Li. 

Flame, — Crimson,  best  obtained  by  gently  heating  near  the  wick. 

INTERFERING  ELEMENTS. 

Sodium^  (a)  Use  a  gentle  flame  and  heat  near  the  wick,  (ft)  Fuse 
on  platinum  wire  with  barium  chloride  in  O.  F.  The  flame  will  be 
first  strong  yellow,  then  green,  and  lastly,  crimson. 

Calcium  or  Strontium. — As  these  elements  do  not  color  the  flame 
in  the  presence  of  barium  chloride,  the  above  test  will  answer. 

Silicon. — Make  into  a  paste  with  boracic  acid  flux  and  water,  and 
fuse  in  the  blue  flame.  Just  after  the  flux  fuses  the  red  flame  will 

appear. 

MAGNESIUM,  Mg. 

On  Coal  with  Soda. — Insoluble,  and  not  absorbed  by  the  coal. 

With  Borax  or  S.  Ph. — Clear  and  colorless  can  be  flamed  opaque- 
white. 

With  Cobalt  Solution* — The  substance  moistened  with  the  solu- 
tion and  heated  strongly  upon  coal  becomes  pale  pink  or  flesh  color. 
^  MANGANESE,  Mn. 

With  Borax  or  S.  Ph.\ — O.  F.  Amethystine  hot,  reddens  on  cool- 


*  With  silicates  this  reaction  is  of  use  only  in  the  absence  of  coloring  oxides.     The 
phosphate,  arsenate  and  borate  become  violet-red. 

i  The  colors  are  more  intense  with  borax  than  with  S.  Ph. 


190  BLOWPIPE  ANALYSIS. 

ing.    With  much,  is  black  and  opaque.     If  a  hot  bead  is 
touched  to  a  crystal  of  sodium  nitrate  an  amethystine  or 
rose-colored  froth  is  formed. 
R.  F.  Colorless  or  with  black  spots. 

With  Soda. — O.  F.  Bluish-green  and  opaque  when  cold.    Sodium 
nitrate  assists  the  reaction. 
, 

INTERFERING  ELEMENTS. 

Chromium. — The  soda  bead  in  O.  F.  will  be  bright  yellowish- 
green  instead  of  bluish-green. 

Silicon. — -Dissolve  in  borax,  then  make  soda  fusion. 

MERCURY,  Hg. 

With  Bismuth  Flux  : 

On  Plaster. — Volatile   yellow   and    scarlet   coat.      If  too 

strongly  heated  the  coat  is  black  and  yellow. 
On  Coal. — Faint  yellow  coat  at  a  distance. 
Closed  Tube  with  Dry  Soda  or  with  Litharge* — Mirror-like 
sublimate,  which  may  be  collected  in  globules. 

MOLYBDENUM,  Mo. 

With  Cone.  H2S04. — The  powder  is  moistened  with  the  acid 
and  evaporated  almost  to  dryness  on  porcelain.  On  cooling,  dark 
blue  spots  are  formed. 

Flame. — Yellowish-green. 

With  Borax.— O.  F.  Yellow  hot,  colorless  cold. 
R.  F.  Brown  to  black  and  opaque. 

With  S.  Ph. — O.  F.  Yellowish-green  hot,  colorless  cold. 
R.  F.  Emerald-green. 

The  bead,  if  saturated  and  crushed,  will  either  stain  damp  un- 
glazed  paper  brown  to  blue  according  to  amount  present  or  if 
dissolved  in  very  dilute  cold  HC1  with  little  metallic  tin,  will  yield 
a  blue  solution  which  becomes  brown  on  heating. 

*  Gold-leaf  is  whitened  by  the  slightest  trace  of  vapor  of  mercury. 


USEFUL   TESTS  WITH  THE  BLOWPIPE.  191 

NICKEL,  Ni. 

With  Dimethylglyoxime. — To  any  solution  containing  nickel, 
add  ammonia,  filter  off*  precipitate  and  to  filtrate  add  a  few  drops 
of  one  per  cent,  solution  of  reagent  in  alcohol.  A  crimson  color 
and  precipitate  results. 

On  Coal. — R.  F.     The  oxide  becomes  magnetic. 

With  Borax. — O.  F.     Violet  hot,  pale  reddish-brown  cold. 

R.  F.      Cloudy  and  finally  clear  and  colorless. 
With  S.  Ph.— O.  F.     Red  hot,  yellow  cold 

R.  F.     Red  hot,  yellow  cold.     On  coal  with  tin  becomes 
colorless. 

INTERFERING  ELEMENTS. 

If  the  dimethyl  reagent  is  available  it  will  be  satisfactory.  If 
not  available  the  methods  of  scorifying  mentioned  under  cobalt 
may  be  used. 

Arsenic. — Roast  thoroughly,  treat  with  borax  in  R.  F.  as  long 
as  it  shows  color,  treat  residual  button  with  S.  Ph.  in  O.  F. 

Alloys. — Roast  and  melt  with  frequently  changed  borax  in  R.  F. 
adding  a  little  lead  if  infusible.  When  the  borax  is  no  longer 
colored,  treat  residual  button  with  S.  Ph.  in  O.  F. 

NITRIC  ACID,  HNO, 

In  Closed  Tube  with  KHSO^. — Brown  fumes  with  characteristic 
odor.  The  fumes  will  turn  ferrous  sulphate  paper  brown. 

PHOSPHORUS,  P. 

With  Ammonic  Molybdate. — This  is  the  surest  test.  See  page 
204. 

Flame. — Greenish-blue,  momentary.  Improved  by  first  dipping 
the  wire  in  concentrated  H2SO4. 

With  Magnesium. — Build  a  pyramid  of  the  powder  on  charcoal 
around  a  half  inch  of  magnesium  ribbon  and  ignite  by  touching 
with  the  flame  ;  then  place  in  water.  The  gas  evolved  will  have 
an  odor  of  putrid  fish. 

POTASSIUM,  K. 

Flame. — Violet,  except  borates  and  phosphates. 


192  BLOWPIPE  ANALYSIS. 

INTERFERING  ELEMENTS. 

Sodium. — (a)  The  flame,  through  blue  glass,  will  be  violet  or 

blue. 
(b)  A  bead  of  borax  and  a  little  boracic  acid,  made 

brown  by  nickel,  will  become  blue  on  addition 

of  a  potassium  compound. 

Lithium. — The  flame,  through  green  glass,  will  be  bluish-green. 
Sodium,  Lithium,  Strontium,  Calcium.     Use  color  screen,  p.  165. 

SELENIUM,  Se. 

On  Coal,  R.  F.  or  in  Closed  Tube. — Disagreeable  horse-radish 
odor,  brown  fumes,  and  a  volatile  steel-gray  coat  with  a  red  border 
(or  dark  red  sublimate). 

On  Coal  with  Soda. — Thoroughly  fuse  in  R.  F.,  place  on  bright 
silver,  moisten,  crush,  and  let  stand.  The  silver  will  be  blackened. 

SILICA,  SiO,. 

Satisfactory  test  needed ;  possibly  the  best  are  as  follows : 

Fuse  with  equal  parts  Na2C03,  K2COZ  on  platinum.  Dissolve 
fused  material  in  dilute  HC1  and  partially  evaporate.  A  jelly 
proves  SiO2. 

With  Cone.  H2SO±  and  CaF2. — If  placed  in  a  lead  cup  and  the 
fumes  condensed  by  a  drop  of  water  upon  a  platinum  wire  a  jelly 
forms  on  the  water. 

With  S.  Ph. — Insoluble.  Silicates  usually  leave  a  translucent 
mass  of  the  shape  of  the  original  fragment.  If  not  decomposed 
by  S.  Ph.,  dissolve  in  borax  nearly  to  saturation,  add  S.  Ph.,  and 
re-heat  for  a  moment.  The  bead  will  become  milky  or  opaque 
white. 

SILVER,  Ag. 

On  Coal. — Silver  minerals  heated  on  charcoal  are  decomposed 
and  a  malleable  "button"  results  which  if  dissolved  in  a  drop  of 
nitric  acid  will  yield  a  white  curd-like  precipitate  on  addition  of  a 
drop  of  hydrochloric  acid. 

Cupellation. — The  only  test  for  a  silver  ore  as  distinct  from  a 
rich  silver  mineral.  See  under  Silver  Minerals. 


USEFUL    TESTS    WITH   THE  BLOWPIPE.  193 

SODIUM,  Na. 

Flame. — Strong  reddish-yellow. 

STRONTIUM,  Sr. 

On  Coal  with  Soda. — Insoluble,  absorbed  by  the  coal. 
Flame. — Intense  crimson,  improved  by  moistening  with  HC1. 
With  Borax  or  S.  Ph. — Clear  and   colorless;  can  be  flamed 
opaque. 

INTERFERING  ELEMENTS. 

Barium. — The  red  flame  may  show  upon  first  introduction  of 
the  sample  into  the  flame,  but  it  is  afterward  turned  brownish- 
yellow. 

Lithium. — Fuse  with  barium  chloride,  by  which  the  lithium  flame 
is  unchanged. 

SULPHUR,  S. 

On  Coal  with  Soda  and  a  Little  Borax. — Thoroughly  fuse  in  the 
R.  F.,  and  either  : 

(a)  Place  on  bright  silver,  moisten,  crush  and  let  stand.    The 

silver  will  become  brown  to  black.     Or, 
(b}  Heat  with  dilute  HC1  (sometimes  with  powdered  zinc)  ; 

the  odor  of  H2S  will  be  observed. 

///  Open  Tube. — Suffocating  fumes.  Some  sulphates  are  unaf- 
fected. 

In  Closed  Tube. — May  have  sublimate  red  when  hot,  yellow  cold, 
or  sublimate  of  undecomposed  sulphide,  or  the  substance  may  be 
unaffected. 

With  Soda  and  Silica  (equal  parts). — A  yellow  or  red  bead. 
To  Determine  Whether  Sulphide  or  Sulphate. — Fuse  with  soda  on 
platinum  foil.     The  sulphide  only  will  stain  silver. 

TELLURIUM,  Te. 

On  Coal. — Volatile  white  coat  with  red  or  yellow  border.  If 
the  fumes  are  caught  on  porcelain,  the  resulting  gray  or  brown 
film  may  be  turned  crimson  when  moistened  with  cone.  H2SO4, 
and  gently  heated. 


1 94  BL O  WPIPE  ANAL  YSIS. 

With  Hot  Cone.  H2S04. — Rich  powdered  material  placed  on 
a  white  porcelain  plate  in  contact  with  a  drop  of  the  hot  acid 
assumes  a  violet  color. 

TIN,  Sn. 

On  Coal  Alone  or  with  Soda  or  Sulphur. —  R.  F.  Strongly 
heated  forms  yellow  coat,  white  cold.  If  moistened  with  cobalt 
solution  and  strongly  heated  the  coat  becomes  bluish  green. 

With  Metallic  Zn  and  HCl. — A  fragment  of  cassiterite,  placed 
in  contact  with  metallic  Zn  in  dilute  HCl,  becomes  coated  with 
metallic  tin. 

INTERFERING  ELEMENTS. 

Lead  or  Bismuth  (Alloys). — It  is  fair  proof  of  tin  if  such  an  alloy 
oxidizes  rapidly  with  sprouting  and  cannot  be  kept  fused. 

Zinc. — On  coal  with  soda,  borax  and  charcoal  in  R.  F.  the  tin 
will  be  reduced,  the  zinc  volatilized ;  the  tin  may  then  be  washed 
from  the  fused  mass. 

TITANIUM,  Ti. 

With  S.  Ph. — O.  F.  Colorless  to  yellow  hot,  colorless  cold, 
R.  F.  After  careful  solution  in  the  O.  F.  the  bead  may  be  made 
violet  by  strong  reduction. 

S.  Ph.  Bead  in  Acids. — If  after  the  careful  solution  in  O.  F.  the 
bead  is  dissolved  by  boiling  in  a  weak  (1:3)  solution  of  sulphuric 
acid  with  a  little  nitric  acid,  the  addition  of  a  few  drops  of  hydrogen 
peroxide  will  produce  a  deep  yellow  color. 

INTERFERING  ELEMENTS. 
Iron. — The  S.  Ph.  bead  in  R.  F.  is  yellow  hot,  brownish-red  cold. 

TUNGSTEN,  W. 

With  S.  Pk.—Q.  F.     Clear  and  colorless. 

R.  F.     Greenish  hot,  blue  cold.     On  long  blowing  or  with 

tin  on  coal,  becomes  dark  green. 

Either  bead  crushed  and  dissolved  in  cone.  HCl  with  metallic 
tin  will  yield  a  deep  blue  solution,  not  destroyed  by  even  consider- 
able dilution  and  on  evaporation  to  syrup  give  a  purple  perman- 
ganate color. 

INTERFERING  ELEMENTS. 
Iron. — The  S.  Ph.  in  R.  F.  is  yellow  hot,  blood-red  cold. 


USEFUL   TESTS  WITH  THE  BLOWPIPE.  19$ 

URANIUM,  U. 

Nitric  Acid  Solution. — Dissolve  in  dilute  HNO3,  make  alkaline 
with  Na2CO3,  filter  and  to  filtrate  add  solution  of  NaOH,  precipi- 
tating yellow  sodium  uranate. 

With  S.  Ph. — O.  F.     Yellow  hot,  yellowish-green  cold. 
R.  F.  emerald-green. 

Photographic  Plate.  * — Wrap  in  the  dark  a  photographic  plate  in 
two  thicknesses  of  black  paper.  On  the  paper  place  a  key.  Just 
above  the  key  suspend  2  or  3  oz.  of  the  ore.  Place  the  whole  in 
light-tight  box.  Avoid  pressure  of  ore  on  key  and  plate. 

After  3  or  4  days  develop  in  the  usual  way. 

Electroscope. — A  test  dependent  upon  the  power  of  radium  to 
discharge  an  electroscope  may  be  made  quantitative.  A  suitable 
electroscope  f  consists  of  two  compartments  ;  one  above  containing 
a  suspended  gold  leaf  in  front  of  which  is  attached  a  reading  micro- 
scope, and  one  below  in  which  the  ore  to  be  tested  is  placed. 
Usually  the  leaf  is  charged  by  means  of  a  piece  of  vulcanite  rubbed 
on  the  sleeve  of  the  coat,  the  charge  causing  the  leaf  to  rise ;; 
then  the  natural  leak  of  electricity  is  noted  on  the  scale  and  calcu- 
lated as  a  certain  number  of  divisions  per  minute.  The  ore  is  then 
placed  in  the  compartment  below  and  the  leak  of  the  leaf  noted  as 
before.  For  example : 

Natural  leak  of  instrument  =    0.5  divisions  per  minute 

Fall  of  leaf  with  3  per  cent.  U3O8  ore  =  48.5         "  " 

Fall  of  leaf  with  ore  tested  =36.5         "  "         " 

Deducting  the  natural  leak  from  each 
UoOs  in  standard  ore  : 

o       o 

U3O8  in  ore  tested  =  48  :  36 

U3O8  in  ore  tested  =  —  - —  =2.2  per  cent. 
45 

INTERFERING  ELEMENTS. 
Iron. — With  S.  Ph.  in  R.  F.  is  green  hot,  red  cold. 

*  Thorium  has  a  decomposition  product,  mesothorium,  which  also  is  radio-active, 
t  Prospector's  Device,  E.  &  M,  J.,  May  16,  1914,  p.  996  or  Bulletin  70,  Bureau 
of  Mines,  p.  26. 


1 96  BL  O  WPIPE  ANAL  YSIS. 

VANADIUM,  V. 

Hydrochloric  Acid  Solution. — Boiled  with  cone.  HC1  gives  a 
brownish-red  solution  which  is  decolorized  by  a  few  drops  of  water 
and  regains  its  color  with  a  few  drops  of  peroxide  of  hydrogen. 

(Patronite  needs  separate  roasting  and  roscoelite  a  previous 
fusion  with  sodium  carbonate.) 

With  S.  Ph.— O.  F.     Dark  yellow  hot,  light  yellow  cold. 
R.  F.     Brown  hot,  emerald-green  cold. 

ZINC,  Zn. 

On  Coal. — R.  F.  Yellow  coat,  white  when  cold.  If  moistened 
with  cobalt  solution  and  strongly  heated  the  coat  becomes  bright 
green. 

It  is  best  to  moisten  the  coal,  in  front  of  the  assay,  with  the  solution,  and  blow  a 
strong  R,  F.  upon  the  assay. 

INTERFERING  ELEMENTS. 

Antimony. — Remove  by  strong  O.  F.,  or  by  heating  with  sul- 
phur in  closed  tube. 

Cadmium  Lead  or  Bismuth. — The  combined  coats  will  not  pre- 
vent the  cobalt  solution  test. 

Tin. — The  coats  heated  in  an  open  tube,  with  charcoal  dust  by 
the  O.  F.,  may  yield  white  sublimate  of  zinc. 


CHAPTER   XIV. 
SCHEMES  FOR  QUALITATIVE  BLOWPIPE  ANALYSIS. 


.*  —  Heat  a  portion  gently  with  0.  F.  upon  charcoal  or  a 
plaster  tablet  which  has  been  blackened  in  the  lamp  flame. 

As.  —  White  very  volatile  crystalline  coat,  white  fumes  having 
garlic  odor  and  invisible  near  assay,  best  on  plaster. 

The  coat  disappears  before  R.  F.,  tingeing  it  pale  blue  and  evolving  the  character- 
istic garlic  odor. 

CONFIRMATION  As.  —  The  coating  may  be  scraped  off  together  with  a  little  charcoal 
and  if  heated  in  closed  tube  should  yield  an  arsenic  mirror  ;  or  it  may  be  dissolved  in 
solution  of  KOH,  placed  in  a  test-tube,  a  small  piece  of  sodium  amalgam  added,  and 
the  tube  covered  with  a  piece  of  filter  paper  moistened  with  a  slightly  acid  solution  of 
AgNO3.  The  paper  will  be  stained  black  by  the  AsH3  evolved. 

Sb.  —  White  fumes  and  white  pulverulent  volatile  coat,  best  on 
charcoal. 

A  good  distinguishing  feature  between  As  and  Sb  is  as  follows  :  They  both  usually 
continue  to  give  off  fumes  after  removal  of  the  flame,  but  while  still  hot  the  As2O3  fumes 
are  not  visible  within  one-half  inch  of  assay,  while  Sb2O4  fumes  appear  to  come  imme- 
diately from  the  mass. 

CONFIRMATION  Sb.  —  The  coating  disappears  before  R.  F.,  tingeing  it  a  pale  yel- 
low-green, or,  if  scraped  together,  dissolved  in  S.  Ph.  and  just  fused  on  charcoal  in 
contact  with  tin  it  will  form  a  gray  or  black  opaque  bead. 

If  the  coating  be  scraped  off  and  dissolved  in  tartaric  acid  -)-  HC1,  and  the  solution 
placed  in  a  platinum  capsule  with  a  piece  of  zinc,  Sb,  if  present,  will  give  a  black 
adherent  stain.  This  may  be  confirmed  by  washing  the  stain  with  water,  then  dissolv- 
ing it  in  a  few  drops  of  hot  tartaric  acid  plus  a  drop  or  two  of  HC1  ;  on  adding  H2S,  an 
orange  precipitate  proves  Sb2S3. 

Most  antimony  minerals  leave  a  white  residue  when  treated  with  concentrated  nitric 
acid.  If  this  residue  is  washed  with  water,  dissolved  in  HC1  and  H2S  added,  an  orange 
precipitate  of  Sb2S.$  will  be  formed. 

TEST  II.  —  Mix  some  of  the  powdered  substance  with  metallic 
sodium  |  by  means  of  a  knife  blade,  ignite  carefully  on  charcoal 
and  heat  residue  with  blowpipe  flame  to  obtain  coatings  or  to  fuse 
together  any  metallic  particles.  \  Or  mix  a  portion  with  soda  and 

*  Test  I.  may  also  yield  white  coating  of  chlorides  or  lead  sulphate,  or  of  Se  or  Te, 
non-volatile  coatings  of  Sn  or  Zn  near  the  assay,  yellow  hot  and  white  cold  ;  yellow 
coatings  of  Pb  or  Bi  ;  crystalline  yellow  and  white  coating  of  Mo  ;  and  deep  brown 
coating  of  Cd.  All  of  these  will  be  detected  with  greater  certainty  by  later  tests. 

fTest  II.  may  also  yield  white  coats  from  Pb,  Bi  or  alkalis,  yellow  coats  from  Pb  or 
Bi,  brown  or  red  coats  from  Cu  or  Mo,  and  the  ash  of  the  coal  may  be  white  or  red. 

J  Until  perfectly  familiar  with  metallic  sodium  reaction  always  read  the  precaution 
on  page  92. 

I97 


198  BLOWPIPE  ANALYSIS. 

a  little  borax  and  heat  strongly  upon  charcoal  with  R.  F.  for  three 
or  four  minutes. 

A.  Volatile  fumes  or  coating  on  charcoal. 

As. — Garlic  odor,  white  fumes  and  a  white  volatile  coat. 

Sb. — White  fumes  and  a  white  volatile  coat. 

Cd. — Dark  brown  volatile  coat,  sometimes  shading  to  greenish- 
yellow  and  usually  surrounded  by  a  variegated  coloration  resem- 
bling the  colors  of  peacock  feathers. 

CONFIRMATION  Cd. — The  coat  forms  at  first  heating,  and,  if  mixed  with  Na2S2O3 
and  fused  in  a  borax  bead,  will  form  a  bright  yellow  mass  of  CdS. 

Zn. — White  not  easily  volatile  coat,  yellow  when  hot. 
Sn. — White  non-volatile  coat  close  to  assay,  yellow  while  hot 
and  usually  small  in  amount. 

CONFIRMATION  Zn  and  Sn. — If  any  coat  forms,  moisten  it  with  cobalt  solution  and 
blow  a  strong  blue  flame  on  the  substance.  The  coatings  from  other  elements  will 
not  prevent  the  cobalt  coloration.  The  zinc  coat  is  made  bright  yellowish-green. 
The  tin  coat  becomes  bluish-green. 

B.  Residue  left  on  charcoal. 

Crush,  pulverize  and  examine  the  residue  for 

I.  Magnetic  particles  ;  2.  Metallic  buttons  ;  3.  On  moist  silver 
coin. 

i.  Collect  any  magnetic  particles  with  the  magnet;  dissolve  some 
of  the  magnetic  particles  in  a  borax  bead  with  the  0.  F.  Try  also 
effect  of  R.  F. 

Fe. — The  bead  is  :  O.  F.  hot,  yellow  to  red ;  O.  F.  cold,  color- 
less to  yellow ;  R.  F.  cold,  bottle-green. 

CONFIRMATION  Fe. — The  magnetic  particles  yield  with  HNO3,  a  brown  solution 
from  which,  after  evaporating  excess  of  acid,  K4FeCy6  throws  down  a  blue  precipi- 
tate. 

Ni. — The  bead  is :  O.  F.  hot,  intense  violet ;  O.  F.  cold,  pale 
brown ;  R.  F.  cold,  colorless. 

CONFIRMATION  Ni. — If  the  excess  of  acid  is  driven  off  by  evaporation,  KCy  added 
in  excess,  and  the  solution  then  made  strongly  alkaline  with  KOH,two  or  three  drops 
of  pure  bromine  will  give  a  black  precipitate  of  Ni2(OH)6. 

Co. — The  bead  is :  O.  F.  and  R.  F.  hot  or  cold,  a  deep  pure 
blue ;  if  greenish  when  hot,  probably  Fe  or  Ni  is  also  present. 

CONFIRMATION  Co. — The  magnetic  particles  yield  with  HNO3,  a  red-rose  solution 
which  becomes  blue  on  evaporation. 


SCHEMES  FOR    QUALITATIVE  ANALYSIS.  199 

2.  Examine  residue  for  metallic  buttons  and  observe  if  they  are 
malleable  or  not.* 

Ag.  —  Silver  white  malleable  button. 

CONFIRMATION  Ag.  —  Dissolve  button  in  dilute  HNO3,  and  add  a  drop  of  HC1.  A 
white  precipitate,  soluble  in  NH4OH  is  obtained. 

Pb.  —  Lead  gray  malleable  button. 

CONFIRMATION  Pb.  —  With  bismuth  flux  on  charcoal  gives  yellow  coating. 

Sn.  —  White  malleable  button. 

CONFIRMATION  Sn.  —  Heated  in  O.  F.  on  charcoal  gives  a  non-volatile  coating, 
yellow  hot  and  white  cold.  Decomposed  in  cone.  HNO3  with  white  residue  of  meta- 
stannic  acid. 

Cu.  —  Reddish  malleable  button. 

CONFIRMATION  Cu.  —  Dissolves  in  HNO3  to  a  green  solution  rendered  intense  blue 
when  neutralized  with  NH4OH. 

Au.  —  Yellow  malleable  button. 

CONFIRMATION  Au. — Insoluble  in  HNO3  or  HC1  alone,  but  dissolved  by  mixed 
acids. 

Bi.  —  Reddish  white  brittle  button. 

CONFIRMATION  Bi.  —  Heat  with  bismuth  flux. 

Sb.  —  White  brittle  button,  yielding  white  coating  before  the 
blowpipe. 

3.  Dig  up  some  of  the  charcoal  beneath  assay,  place  upon  a  bright 
silver  surface ;  moisten  with  water  and  let  stand. 

S,  Se,  Te. — The  bright  silver  is  stained  black  or  dark-brown, 
and  unless  the  horseradish  odor  of  Se  or  the  brown  coatings  of 
Se  and  Te  with  bismuth  flux  have  been  already  obtained,  this  stain 
will  prove  sulphur. 

CONFIRMATIONS  S. — The  soda  fusion  will  evolve  H2S  when  moistened  with  HC1. 
By  holding  in  the  gas  a  piece  of  filter  paper  moistened  with  a  drop  or  two  of  lead 
acetate  (test  is  made  more  sensitive  by  adding  a  drop  of  ammonia  to  the  acetate),  the 
paper  will  be  stained  black. 

CONFIRMATION  Se.— Characteristic  disagreeable  horseradish  odor  during  fusion. 

CONFIRMATIONS  Te. — If  a  little  of  the  original  substance  is  dropped  into  boiling 
concentrated  H2SO4,  a  deep  violet  color  is  produced;  this  disappears  on  further 
heating. 

The  quite  cold  soda  fusion  added  to  hot  water  produces  a  purple-red  solution. 

TEST  III. — Mix  a  portion  of  the  substance  with  more  than 
an  equal  volume  of  bismuth  flux,f  and  heat  gently  upon  a 
plaster  tablet  with  the  oxidizing  flame. 

*  A  white  malleable  button  of  zinc  is  sometimes  obtained  but  not  if  reduction   wa? 
made  by  soda.      It  is  easily  soluble  in  cold  dilute  hydrochloric  acid  with  effervescence, 
f  Formed  by  grinding  together  I  part  KI,  I  part  KHSO4,  2  parts  S. 


200  BLOWPIPE  ANALYSIS. 

Pb. — Chrome-yellow  coat,  darker  hot,  often  covering  the  entire 
tablet. 

CONFIRMATION  Pb. — If  the  test  is  made  on  charcoal,  the  coat  is  greenish-yellow, 
brown  near  the  assay. 

Hg. — Gently  heated,  bright  scarlet  coat,  very  volatile,  and  with 
yellow  fringe ;  but  if  quickly  heated,  the  coat  formed  is  pale  yel- 
low and  black. 

CONFIRMATION  Hg. — If  the  substance  is  heated  gently  in  a  closed  tube  or  matrass 
with  dry  soda  or  litharge,  a  mirror-like  sublimate  will  form,  which  may  be  collected 
into  little  globules  of  Hg  by  rubbing  with  a  match  end.  The  test  with  bismuth  flux 
on  charcoal  yields  only  a  faint  yellow  coat. 

Bi. — Bright  chocolate-brown  coat,  with  sometimes  a  reddish 
fringe. 

CONFIRMATIONS  Bi. — The  coat  is  turned  orange-yellow,  then  cherry-red,  by  fumes 
of  NH3,  which  may  conveniently  be  produced  by  heating  a  few  crystals  of  S.  Ph.  on 
the  assay.  The  test  with  bismuth  flux  on  charcoal  yields  a  bright-red  band,  with 
sometimes  an  inner  fringe  of  yellow. 


Sb 


. — Orange  to  peach-red  coat,  very  dark  when  hot. 


CONFIRMATION  Sb. — The  coat  becomes  orange  when  moistened  with  (NH4)2S. 

Test  III.  may  yield  colored  sublimates  with  large  amounts  of  certain  other  elements, 
and  on  smoked  plaster  certain  white  sublimates  are  obtainable.  In  all  cases  the 
elements  are  detected  with  greater  certainty  by  other  tests,  but  for  convenience  they 
are  here  summarized :  Sn,  brownish-orange ;  As,  reddish-orange ;  Se,  reddish-brown ; 
Te,  purplish-brown,  with  deep  brown  border ;  Mo,  deep  ultramarine  blue ;  Cu,  Cd, 
Zn,  white  on  smoked  plaster. 

TEST  IV.— Dissolve  substance  in  salt  of  phosphorus  in  O.  F. 
so  long  as  bead  remains  clear  on  cooling.  Treat  then  for 
three  or  four  minutes  in  a  strong  R.  F.  to  remove  volatile 
compounds.  Note  the  colors  hot  and  cold,  then  re-oxidize 
and  note  colors  hot  and  cold. 

Fe,  Ti,  Mo,  W. — The  bead  in  O.  F.  cold  is  COLORLESS  or  very 

FAINT  YELLOW. 

CONFIRMATION  Fe. — The  bead  in  its  previous  treatment  should  have  been  O.  F. 
hot,  yellow  to  red  ;  O.  F.  cold,  colorless;  R.  F.  cold,  red. 

CONFIRMATION  Ti. — The  bead  is  reduced  on  charcoal  with  tin,  pulverized  and  dis- 
solved in  \  HC1  with  a  little  metallic  tin.  The  reduced  bead  is  violet,  the  solution  is 
violet  and  turbid. 

CONFIRMATIONS  Mo. — Tested  as  above  on  charcoal  with  tin,  etc.,  the  reduced  bead 
is  green,  the  solution  is  dark  brown.  Heat  a  little  of  the  substance  on  platinum  foil 
with  a  few  drops  of  cone.  HNOS,  heat  until  excess  of  HNOq  has  all  volatilized,  then  add 


SCHEMES  FOR    QUALITATIVE  ANALYSIS.  2OI 

few  drops  of  strong  H2SO4  and  heat  until  copious  fumes  are  evolved  ;  cool,  and  breathe 
upon  the  cooled  mass ;  an  ultramarine  blue  =  Mo. 

CONFIRMATION  W. — Tested  on  charcoal  with  tin,  etc.,  as  above,  the  reduced  bead 
is  green,  the  solution  is  deep  blue. 

Ur,  V,  Ni.* — The  bead  in  O.  F.  cold,  is  colored  YELLOW  OR 

GREENISH-YELLOW. 

CONFIRMATION  U. — The  bead  in  R.  F.  is  dull  green,  hot;  fine  green,  cold.  Make 
a  Na2CO3  fusion,  dissolve  in  HC1  or  H2SO4,  add  a  few  drops  or  H2S  water,  and  if  it 
gives  any  precipitate,  add  it  in  excess  and  filter;  to  filtrate  add  a  few  drops  of  HNO3 
and  boil,  then  add  NH4OH  to  alkaline  reaction,  filter,  wash  precipitate  with  ammonia 
water,  and  then  treat  precipitate  with  a  concentrated  solution  of  (NH4)2CO3  -f  NH4OH, 
filter,  acidify  filtrate  with  HC1,  and  add  K4FeCy6.  Brown  ppt.  =  Ur. 

CONFIRMATION  V. — In  R.  F.  the  bead  will  be  brownish  hot,  fine  green  cold.  Fuse 
substance  with  Na2CO3  in  O.  F.,  and  dissolve  fusion  in  a  few  drops  of  dilute  H2SO4 
or  HC1,  add  a  piece  of  zinc  and  warm;  blue  color  changing  to  green  and  finally  vio- 
let =  V. 

CONFIRMATION  Ni. — A  borax  bead  in  O.  F.  will  be  intense  violet,  and  in  R.  F.  will 
be  reddish  hot,  yellow  cold. 

Mn. — The  bead  in  O.  F.,  cold,  is  colored  VIOLET  ;  if  touched 
while  hot  to  a  crystal  of  nitre,  it  is  made  deep  permanganate  color. 

CONFIRMATION  Mn. — Fused  on  platinum  wire  in  O.  F.,  with  a  paste  of  soda,  and 
nitre,  manganese  yields  an  opaque  bluish-green  bead. 

Cr. — The  bead  in  O.  F.,  cold,  is  colored  GREEN. 

*  If  the  absence  of  Ni  is  not  proved,  or  Co  obscures  the  tests,  dissolve  the  substance 
in  borax  on  charcoal  to  saturation,  and  treat  for  five  minutes  in  hot  R.  F. 

If  a  visible  button  results,  separate  it  from  the  borax,  and  treat  with  S.  Ph.  in  the 
O.  F.,  replacing  the  S.  Ph.  when  a  color  is  obtained. 

If  no  visible  button  results,  add  either  a  small  gold  button  or  a  few  grains  of  test 
lead.  Continue  the  reduction,  and,  if  lead  has  been  used,  scorify  the  button  with  fre- 
quently changed  boracic  acid  to  small  size,  stopping  the  instant  the  boracic  acid  is 
colored  by  Co,  Ni,  or  Cu,  blue,  yellow,  or  red,  respectively. 

Complete  the  removal  of  lead  by  O.  F.  on  coal,  and  treat  as  below. 

Treat  the  gold  alloy,  or  the  residual  button  from  the  lead  alloy,  on  coal,  with  fre- 
quently changed  S.  Ph.,  in  strong  O.  F. 

The  metals  which  have  united  with  the  gold  or  lead,  will  be  successively  oxidized 
and  their  oxides  will  color  the  S.  Ph.  in  the  following  order  : 

Co. — Blue,  hot;  blue,  cold.     May  stay  in  the  slag. 

Ni. — Brown,  hot;  yellow,  cold.     May  give  green  with  Co  or  Cu. 

Cu. — Green,  hot ;  blue,  cold.     Made  opaque  red  by  tin  and  R.  F. 

The  slag  should  contain  the  more  easily  oxidizable  metals,  and  be  free  from  Cu, 
Ni,  and  Ag.  Test  a  portion  with  S.  Ph.  and  tin  to  prove  absence  of  Cu.  If  present,  it 
must  be  removed  by  further  reduction  with  lead.  Pulverize  the  slags  and  dissolve  a 
portion  in  S.  Ph.,  and  examine  by  Tgst  V. 


202  BLOWPIPE  ANALYSIS. 

There  may  be  a  green  bead  from  admixture  of  a  blue  and  a  yellow.  If  Cr  is  not 
proved,  examine  in  such  a  case  for  Ur,  V,  Cr,  etc.,  with  unusual  care. 

CONFIRMATION  Cr. — If  the  substance  is  fused  on  platinum  wire  in  the  O.F.  with  a 
paste  of  soda  and  nitre,  an  opaque  yellow  bead  is  produced  ;  and  if  the  soda  bead  is 
dissolved  in  water,  filtered,  acidified  with  acetic  acid,  and  a  drop  or  two  of  lead 
acetate  added,  a  yellow  precipitate  will  be  formed. 

Co,  Cu. — The  bead  in  O.  F.?  cold,  is  colored  BLUE. 

CONFIRMATION  Co.— The  bead  is  deep  blue,  hot  and  cold,  in  both  flames. 

CONFIRMATION  Cu. — The  bead  is  green,  hot,  greenish-blue,  cold,  and  on  fusion  with 
tin  on  coal  becomes  opaque  brownish-red.  • 

With  larger  percentage  of  copper,  the  substance  will  yield  a  mixed  azure-blue  and 
green  flame  on  heating  with  HC1. 

SiO2,  A12O3,  TiO2,  SnO2 — The  saturated  bead  contains  an  ap- 
preciable amount  of  INSOLUBLE  MATERIAL,  in  the  form  of  a  trans- 
lucent cloud,  jelly-like  mass,  or  skeleton  form  of  the  original 
material. 

CONFIRMATION  SiO2, — Mix  the  dry  substance  with  a  little  dry  calcium  fluoride 
free  from  SiO2,  place  in  platinum  dish,  add  cone.  H.2SO4  and  heat  gently,  hold  in  fumes 
given  off,  a  drop  of  water  in  loop  of  platinum  wire  ;  SiO3  will  be  separated  on  coming 
in  contact  with  the  water  and  form  a  jelly-like  mass. 

Silica  or  silicates  fused  with  soda  unite  with  noticeable  effervescence. 

CONFIRMATION  A12O3,  TiO2,  SnO2,  SiO2. — If  infusible,  moisten  the  pulverized 
mineral  with  dilute  cobalt  nitrate  solution  and  heat  strongly. 

A12O3.— Beautiful  bright  blue. 

TiO2.— Yellowish  green. 

SnO3. — Bluish  green. 

SiO2. — Faint  blue ;  deep  blue,  if  fusible. 

There  may  also  be  blues  from  fusible  phosphates  and  borates,  greens  from  oxides 
of  Zn,  Sb,  violet  from  Zr,  various  indefinite  browns  and  grays,  and  a  very  character- 
istic pale  pink  or  flesh  color  from  Mg. 

CONFIRMATION  SnO2.— Treat  the  finely  pulverized  mineral  with  Zn  and  HC1  in 
contact  with  platinum.  Dissolve  any  reduced  metal  in  HC1  and  test  with  HgCl2. 
There  will  be  white  or  gray  ppt. 

Ba,  Ca,  Sr,  Mg. — The  saturated  bead  is  WHITE  and  OPAQUE 
and  the  nearly  saturated  bead  can  be  flamed  white  and  opaque. 

CONFIRMATION  Ba,  Ca,  Sr.— Moisten  the  flattened  end  of  a  clean  platinum  wire 
with  dilute  hydrochloric  acid,  dip  it  in  the  roasted  substance,  and  heat  strongly  at  the 
tip  of  the  blue  flame,  and  gently  near  the  wick.  Remoisten  with  the  acid  frequently. 

Ba. — Yellowish-green  flame,  bluish-green  through  green  glass. 

Ca. — Yellowish-red  (brick-red)  flame,  green  through  green  glass. 

Sr. — Scarlet-red  flame,  faint  yellow  through  green  glass. 

There  may  also  be   produced  Li,  carmine-red-flame,  invisible  through  green  glass. 


SCHEMES  FOR    QUALITATIVE  ANALYSIS.  203 

K,  rose-violet  flame,  reddish-violet  through  blue  glass.  Na,  orange-yellow  flame, 
invisible  through  blue  glass.  Cu.  azure-blue  and  emerald  green.  Se  and  As,  pale 
blue.  Mo,  Sb,  Te,  pale  green. 

CONFIRMATION  Mg. — Moisten  the  roasted  substance  with  cobalt  solution,  and  heat 
strongly.  The  substance  will  be  colored  pale  pink  or  flesh  color,  or  violet  if  present 
as  either  arsenate  or  phosphate  or  borate. 

TEST  V. — Cupellation  for  silver  and  gold.  Fuse  one  vol. 
of  the  roasted  substance  on  charcoal  with  i  vol.  of  borax  glass, 
and  i  to  2  vols.  of  test  lead  in  R.  F.  for  about  two  minutes. 
Remove  button  and  scorify  it  in  R.  F.  with  fresh  borax,  then 
place  button  on  cupel  and  blow  O.  F.  across  it,  using  as  strong 
blast  and  as  little  flame  as  are  consistent  with  keeping  the 
button  melted.  If  the  litharge  is  dark,  or  if  the  button  freezes 
before  brightening,  or  if  it  brightens  but  is  not  spherical,  re- 
scorify  it  on  charcoal  with  borax,  add  more  test  lead,  and 
again  cupel  until  there  remains  only  a  bright  spherical  button 
unaltered  by  further  blowing. 

Ag. — The  button  is  white. 

Au. — The  button  is  yellow  or  white. 

CONFIRMATION  Ag  AND  Au. — Dissolve  in  a  drop  of  HNO3,  and  add  a  drop  of 
HC1,  producing  a  white  curd-like  precipitate.  If  gold  is  present  there  will  be  a  resi- 
due insoluble  in  HNO3  which  will  become  golden  yellow  on  ignition. 

TEST  VI. — Heat  substance  in  matrass  with  acid  potassium 
sulphate. 

N2O6,  Br.— Reddish  brown  vapor. 

CONFIRMATION  N2O5. — The  gas  turns  ferrous  sulphate  paper  brown.  Nitrates  defla- 
grate violently  when  fused  on  charcoal. 

Cl. — Colorless  or  yellowish  green  vapor,  with  odor  of  chlorine. 
I. — Violet  choking  vapor. 

CONFIRMATION  Br,  Cl,  I.— Saturate  a  salt  of  phosphorus  bead  with  CuO,  add  sub- 
stance, and  treat  in  O.  F.  Br,  azure  blue  and  emerald  green  flame.  Cl,  azure  blue 
flame  with  a  little  green.  I,  emerald  green  flame. 

Fuse  with  Na2CO3,  pulverize  and  mix  with  MnO2,  and  add  a  few  drops  of  cone. 
H2SO4,  and  heat.  Cl,  yellowish  green  gas  that  bleaches  vegetable  colors.  Br,  red 
fumes. 

Fuse  with  Na2CO3,  dissolve  in  water,  make  slightly  acid  with  H2SO4,  and  add 
Fe2(SO4)3  (ferric  alum  nay  be  used),  and  boil ;  I,  violet  fumes  (turn  starch  paper 
blue). 


204  BLOWPIPE  ANALYSIS. 

F. — The  glass  of  the  matrass  is  corroded,  and  if  SiO2  is  present 
a  film  of  SiO2  is  often  deposited  on  the  glass. 

CONFIRMATION  F. — If  the  substance  be  mixed  with  silica  and  then  heated  with 
Concentrated  sulphuric  acid,  and  the  fumes  caught  on  a  drop  of  water  held  in  a  loop  of 
platinum  wire,  gelatinous  silica  will  form  in  the  water. 

TEST  VII. — Heat  the  substance  gently  with  water  to  re- 
move air  bubbles  and  then  with  dilute  hydrochloric  acid. 

CO2. — Effervescence  continuing  after  heat  is  removed. 

H2S,  Cl  and  H  are  sometimes  evolved,  but  usually  the  odor  will  distinguish 
these. 

CONFIRMATION  CO2. — If  the  gas  is  passed  into  lime  water,  a  white  cloud  and  ppt. 
will  be  produced. 

TEST  VIII. -Place  a  piece  of  Mg  -wire  in  a  closed  tube,  and 
cover  the  -wire  with  a  mixture  of  soda  and  the  substance. 
Heat  till  the  mass  takes  fire,  cool  and  add  water. 

P. — Evolution  of  phosphine,  recognized  by  odor. 

CONFIRMATION  P.— Fuse  a  little  of  the  substance,  previously  roasted  if  it  contains  As, 
with  two  or  three  parts  Na2CO3  and  one  of  NaNO3  dissolve  in  HNO3,  and  add  excess  of 
(NH4)2MoO4;  yellow  ppt.  =  P2O5.  In  presence  of  SiO2  it  is  well  to  confirm  this  ppt. 
by  dissolving  it  in  dilute  NH4OH,  allowing  it  to  stand  for  half  an  hour  and  filtering 
off  any  SiO2  that  separates,  then  to  filtrate  adding  magnesia  mixture  (MgCl2  -(- 
NH4C1  +  NH4OH) ;  white  ppt.  =  P2O5. 

Phosphates  yield  a  pale  momentary  bluish  green  flame  when  moistened  with  con- 
centrated H2SO4  and  treated  at  the  tip  of  the  blue  flame. 

TEST  IX.— Make  a  paste  of  four  parts  KHSO4,  one  part  CaF2, 
•water  and  substance.  Treat  at  tip  of  blue  flame.  Just  after 
water  is  driven  off  the  flame  will  be  colored. 

B. — Bright  green. 
Li. — Carmine. 

CONFIRMATION  B.  —  Heat  some  of  the  substance  gently  on  platinum  wire,  then  add 
a  drop  of  concentrated  H2SO4,  heat  very  gently  again,  just  enough  to  drive  off  exces 
of  H2SO4,  dip  in  glycerine,  hold  in  flame  until  glycerine  begins  to  burn,  remove  from 
flame,  and  the  mass  will  continue  burning  with  a  green  flame.  Turmeric  paper,  moist- 
ened with  an  HC1  solution  containing  boron  and  dried  at  100°,  is  turned  a  reddish 
brown  which  ammonia  blackens. 

TEST  X.  —  Make  a  paste  of  the  powdered  substance  with  strong 
HC1.  Treat  on  platinum  wire  in  the  non-luminous  flame  of  a 
Bunsen  burner.  Confirm  results  by  the  spectroscope  as  directed  on 
page  87. 


SCHEMES  FOR    QUALITATIVE  ANALYSIS.  205 

The  color  imparted  to  the  flame  is : 

Alone.  Through  blue  glass. 

Na,  Yellow.                           Invisible  or  pale  blue. 

K,  Violet.                              Reddish  violet. 

Na  and  K,  Yellow.                           Reddish  violet. 

Ba,  Mo,  B,  Yellowish  green.           Bluish  green. 

Ca,  Red.                                 Greenish  gray. 

Sr,  Scarlet.                            Violet. 

f  Azure  blue,         )  J  Azure  blue. 

'  '  [  Emerald  green,  j  [  Emerald  green. 

TEST  XL  — Heat  the  substance  in  a  closed  tube.* 

H00.  —  Moisture  on  the  side  of  tube. 

Hg.  —  Metallic  mirror  collecting  in  globules. 

As.  —  Metallic  mirror  but  no  globules. 

TEST  XILf  —  Treat  the  finely  powdered  substance  in  a  test-tube 
with  strong  HC1.  Observe  the  result,  then  boil. 

Effervescence.  —  If  the  substance  is  non-metallic  the  gas  given 
off  will  almost  always  be  CO2  showing  that  the  substance  was  a 
carbonate.  .  H2S  is  easily  recognized  by  its  odor.  Cl  which  is 
yellowish  and  very  offensive  would  be  given  off  only  in  a  few  cases 
by  the  action  of  some  oxides  on  HC1. 

CONFIRMATION  C0.r  — A  drop  of  lime  water  on  the  end  of  a  glass  rod  held  in  the 
gas  after  it  has  been  passed  through  water  to  free  it  from  HC1  will  be  rendered  turbid. 

CONFIRMATION  H2S.  —  A  piece  of  filter  paper  moistened  with  lead  acetate  will  be 
blackened  if  held  in  the  gas. 

CONFIRMATION  Cl.  —  A  piece  of  moistened  red  litmus  paper  held  in  the  gas  will  be 
bleached. 

Gelatinous  Residue.  —  If  a  gelatinous  residue  forms  after  boiling 
away  the  larger  part  of  the  acid  a  silicate  was  present. 


*  Other  sublimates  may  result  as  noted  on  page  94. 
|  Substitute  for  test  VII.  when  convenient. 


206  BLOWPIPE  ANALYSIS. 

SPECIAL    SCHEME    FOR    DETECTION   OF  THOSE 
METALS  WHICH  WHEN  PRESENT  AS  SILI- 
CATES   USUALLY     FAIL     TO    YIELD 
SATISFACTORY  TESTS  BEFORE 
THE  BLOWPIPE. 

Remove  the  volatile  constituents  as  thoroughly  as  possible  by 
roasting,  then  heat  gently  in  a  platinum  capsule,  with  HF  and  a 
few  drops  of  concentrated  H2SO4  as  long  as  fumes  are  given  off; 
add  a  little  more  HF  and  H2SO4,  and  heat  again  in  the  same  way. 
When  fusion  is  quite  cold,  dissolve  in  cold  water  and  filter. 

Filtrate  a. — Divide  into  four  parts  and  test  as  follows : 

1.  Add  a  piece  of  Zn  or  Sn  and  a  little  HC1,  and  heat. 
Ti. — A  violet  or  blue  solution. 

.  CONFIRMATIONS  Ti.— Nearly  neutralize  solution,  and  then  add  Na2S2O3,  and  boil. 
White  ppt.  =  Ti. 

Or,  make  solution  slightly  alkaline,  and  then  acidify  slightly  with  HC1,  and  add 
NaaHPO4.  White  ppt.  =  Ti. 

2.  Add  excess  of  KOH  or  NaOH,  boil  and  filter,  and  to  filtrate 
add  excess  of  NH4C1.  and  boil. 

Al. — White  precipitate. 

Dissolve  ppt.,  produced  by  the  KOH  or  NaOH,  in  HC1,  and 
add  K4FeCy6. 

Fe. — Blue  precipitate. 

3.  Add  HC1 ;  then  make  alkaline  with  NH4OH  and  add  (NH4\S 
-j-(NH4)2CO3  in  slight  excess,  filter;  to  filtrate  add  Na2HPO4. 

Mg. — White  crystalline  precipitate. 

CONFIRMATION  Mg. — If  phosphates  are  present,  this  test  would  not  be  reliable  for 
Mg.  In  such  cases  test  a  few  drops  of  the  solution  with  H2S;  if  it  causes  any  precipi- 
tate, saturate  the  whole  of  the  solution  with  it,  filter,  and  to  nitrate  add  a  few  drops 
of  HNOS,  and  boil  to  oxidize  FeO,  nearly  neutralize  with  solution  of  Na2CO3.  If 
iron  is  not  present,  add  a  few  drops  of  Fe2Cl6,  enough  to  give  a  red  precipitate  with 
the  sodium  acetate,  then  dilute  and  add  excess  of  sodium  acetate,  and  boil,  filter,  and 
to  filtrate  add  NH4OH  -f.  (NH4)2S,  filter,  to  filtrate  add  Na2HPO4.  White  crystalline 
precipitate  =  Mg. 

4.  Add  BaG2  as  long  as  it  gives  a  precipitate,  then  Ba(OH)2  to 
alkaline  reaction,  boil,  filter,  and  to  filtrate  add  (NH4)2CO3  and 
NH4OH  and  heat,  filter;  evaporate  filtrate  to  dryness  and  ignite 
to  drive  out  NH4  salts.     Test  residue  in  flame  for  K  and  Na ;  dis- 
solve residue  in  a  few  drops  of  water,  filter  if  necessary,  and  then 
add  solution  of  PtCl4  and  alcohol. 


SCHEMES  FOR    QUALITATIVE  ANALYSIS.  2O/ 

K.  —  Yellow  crystalline  precipitate. 

CONFIRMATION  Na,  K. — Mix  i  part  of  the  silicate  with  5-6  parts  of  precipitated 
CaCO3  and  I  part  of  NH4C1,  heat  to  redness  in  platinum  capsule  for  thirty  minutes 
being  careful  to  apply  heat  gently  at  first,  digest  sintered  mass  in  hot  water,  and  filter ; 
to  filtrate  add  (NH4)2CO3  and  NH4OH,  heat  and  filter,  evaporate  filtrate  to  dryness  and 
ignite  gently  until  all  ammonium  salts  are  driven  off,  then  determine  Na  and  K  as 
above. 

Residue  a — Boil  with  strong  solution  of  (NH4)2SO4  and  filter. 

Filtrate  b. — Add  a  few  drops  of  H2S  water ;  if  any  precipitate 
forms,  saturate  with  H2S  and  filter,  and  to  filtrate  add  NH4OH 
and  (NH4)2C2C>4. 

Ca. — A  white  precipitate. 

Residue  b. — Moisten  with  concentrated  HC1  and  try  coloration 
of  flame. 

Ba. — Yellowish-green  flame. 

Sr.— Scarlet  flame. 

CONFIRMATION  Ba  and  Sr. — Fuse  residue  b  with  two  to  three  pts.  of  soda  in  a  pla- 
tinum capsule :  treat  fusion  with  boiling  water,  filter,  reject  filtrate,  dissolve  residue 
in  acetic  acid,  add  a  few  drops  of  H2S  water,  if  it  gives  any  precipitate,  saturate  with 
H2S  and  filter,  and  to  filtrate  add  K2Cr2O7.  Ba  =  yellow  precipate.  Filter,  and  to 
nitrate  add  CaSO^  warm  and  let  stand.  Sr  =  white  precipitate. 


PART  III. 


MINERALOGY. 

CHAPTER  XV. 
DEFINITION  AND  PHYSICAL  CHARACTERS   OF  MINERALS. 

Definition  of  a  Mineral. 

The  solid  crust  of  the  earth  is  composed  principally  of  "  min- 
erals "  each  of  which  may  be  broadly  defined  as  a  homogeneous 
substance  of  definite  chemical  composition,  found  ready-made  in  na- 
ture, and  not  directly  a  product  of  the  life  or  the  decay  of  an  organ- 
ism. Usually  also  it  will  possess  a  definite  and  characteristic  crys- 
talline structure. 

The  definition  excludes  laboratory  products  and  natural  sub- 
stances of  organic  origin. 

Laboratory  products  and  natural  products  may  differ  only  in  origin  ;  for  example, 
ice  of  the  pond  and  the  factory,  natural  and  synthetic  ruby.  The  line  is  arbitrarily  drawn. 

Natural  Substances  of  Organic  Origin.— Materials  which  have  formed  part  of  living 
organisms,  coal,  chalk,  pearls,  coral,  shells,  etc.,  are  not  minerals.  If  by  natural 
agencies  their  organic  structure  is  lost  and  a  crystalline  structure  obtained  or  if  their  com- 
ponents recombine  or  combine  with  other  elements,  the  new  substances  are  minerals. 

The  Definite  Chemical  Composition. 

The  composition  of  a  homogeneous  mineral  may  vary  by  a  series 
of  replacements  as  explained  under  Isomorphism,  p.  232,  or  in  the 
case  of  "  Gel  Minerals,"  p.  235,  may  vary  from  taking  up  (adsorb- 
ing) other  substances.  In  the  former  case  a  formula  can  be  figured 
from  the  analysis,  in  the  latter  it  is  difficult  or  impossible. 

The  Characteristic  Crystalline  Structure. 

This  is  a  less  constant  attribute  than  was  believed.  While  it  is 
true  that  most  minerals  occur  usually  in  the  crystalline  condi- 

208 


PHYSICAL   CHARACTERS.  209 

tion,  it  is  a  recognized  fact  that  under  proper  conditions  they  occur 
in  the  amorphous  condition  either  glassy  or  as  a  "  gel  mineral." 

The  Crystalline  Condition. — A  mineral  is  sometimes  defined  as  a  natural  crystal, 
that  is,  possessing  a  crystalline  structure  and  occurring  either  in  crystals  of  characteristic 
shapes  or  in  masses  made  up  of  many  little  crystals  so  crowded  together  that  the  shapes 
are  not  evident. 

In  the  crystal  and  in  each  grain  of  the  aggregation  the  crystalline  structure  will  be 
shown  by  the  constancy  of  the  properties  in  parallel  directions  and  their  variation  in 
directions  not  parallel. 

The  Amorphous  Condition. — It  has  become  recognized  that  quite  a  number  of 
minerals  have  never  been  found  in  crystals  and  in  the  mass  fail  to  show  any  regular 
crystalline  structure.  Such  minerals  are  said  to  be  amorphous.  Usually  they  are  "Gel 
minerals,"  products  of  weathering  or  hot  springs  action,  which  by  their  lack  of  uniform 
composition,  generally  amorphous  structure  and  external  appearance,  suggest  that  they 
are  products  of  colloidal  origin.  Opal  is  the  best  example. 

The  obsidians  and  the  glassy  inclusions  in  volcanic  rocks  are  quickly  cooled 
magma,  that  is,  they  are  essentially  minerals  in  solution. 

The  Study  of  Minerals  or  "  Mineralogy." 

Mineralogy  considers  the  one  thousand  or  so  definite  minerals 
and  the  many  thousands  of  varieties  and  doubtful  species  which 
constitute  the  solid  crust  of  the  earth.  Its  purpose  is  the  study  of 
all  the  qualities  of  these  minerals  ;  their  chemical  composition  as 
revealed  by  analyses  ;  their  molecular  structure  as  revealed  by 
crystalline  form  and  by  physical  tests,  and  their  origin  and  mode 
of  formation  as  revealed  by  associated  minerals,  the  alterations 
which  they  undergo  and  their  synthetic  production. 

In  elementary  work  in  mineralogy,  especially  in  a  technical 
course,  the  principal  object  is  the  acquisition  of  an  "  eye  knowledge  " 
of  the  common  and  commercially  important  minerals  so  that  they 
may  be  recognized  at  sight  or  determined  rapidly  by  a  few  simple 
tests.  This  knowledge  can  be  acquired  only  by  handling  and  test- 
ing many  labelled  and  unlabelled  specimens,  and  is  best  preceded 
by  a  thorough  drill  in  the  use  of  the  blowpipe  and  a  'study  of 
models  and  natural  crystals.  With  this  there  should  be  gained  a 
knowledge  of  their  characters,  economic  uses  and  occurrence. 

THE  PHYSICAL  CHARACTERS  OF  MINERALS. 

Minerals  being  for  the  most  part  in  the  crystalline  condition, 
the  geometric  and  optical  characters  described,  pages  I  to  155, 
constitute  their  most  important  physical  characters.  The  term  is, 
however,  very  commonly  used  for  the  temaining  physical  charac- 
ters described  in  the  following  pages  and  often  subdivided  into 
15 


210  MINERALOGY.  » 

groups,   such  as  characters  dependent  on  light,   or  cohesion  or 
general  characters,  etc. 

LUSTRE. 

THE  lustre  of  a  mineral  is  dependent  upon  its  refractive  power, 
its  transparency  and  its  structure.  It  may  be  called  the  kind  of 
brilliancy  or  shine  of  the  mineral. 

METALLIC  lustre  is  the  lustre  of  metals.  It  is  exhibited  only  by 
opaque  minerals,  and  these,  with  the  exception  of  the  native  metals, 
have  a  black  or  nearly  black  streak. 

Some  authorities*  make  this  very  important,  using  the  streak  to  confirm  the  lustre. 
It  can,  however,  be  used  safely  only  in  one  direction.  If  the  streak  is  essentially  black 
the  lustre  is  metallic,  but  the  green  streak  of  alabandite,  the  brownish  red  of  specular 
hematite,  the  copper  red  of  native  copper,  the  pale  greenish  gray  of  molybdenite,  do 
not  prevent  their  lustre  being  metallic. 

NON-METALLIC  lustre  is  exhibited  by  all  transparent  or  trans- 
lucent minerals.  It  may  be  vitreous,  adamantine,  resinous,  pearly, 
silky,  greasy  or  waxy. 

Vitreous.  —  The  lustre  of  a  fracture  surface  of  glass  or  of  a 
quartz  crystal.  Index  of  refraction  n  =  1.3  to  1.8. 

Adamantine.  — The  almost  metallic  lustre  of  the  uncut  diamond, 
zircon  or  cerussite,  exhibited  by  minerals  of  high  index  of  refrac- 
tion, n  —  1.9  to  2.5. 

Resinous.  —  The  lustre  of  resin  or  sphalerite. 

Greasy.  — The  lustre  of  oiled  glass  or  elaeolite.     n  =  1.7  to  1.9. 

Pearly.  —  The  lustre  of  the  mother  of  pearl  or  of  foliated  talc. 
Common  parallel  to  a  very  perfect  cleavage. 

Silky.  —  The  lustre  of  silk  or  of  satin  spar,  due  to  a  fibrous 
structure. 

Dull.  —  Without  lustre  or  shine  of  any  kind.  Kaolin  or  chalk 
are  good  examples. 

The  prefix  sub,  as  sub-metallic,  sub-vitreous,  is  used  to  express 
an  imperfect  lustre  of  the  kind. 

The  words  splendent,  shining,  glistening,  glimmering  and  dull 
are  terms  of  intensity  dependent  on  the  quantity  of  light  reflected. 

Lustre  should,  when  possible,  be  determined  by  a  comparison 
with  minerals  of  known  lustre,  and  should  always  be  observed  on 
a  fresh  or  unaltered  surface. 

The  degree  and  kind  of  lustre  are  always  the  same  on  like  faces 

*  Brush-Penfield,  Determinative  Mineralogy,  p.  226 ;  Dana-Ford,  p.  66. 


PHYSICAL  CHARACTERS.  211 

of  the  crystal,  but  may  be  different  on  unlike  faces,  as  in  apophyllite, 
which  has  pearly  basal  pinacoid  and  vitreous  prism  faces. 

COLOR. 

The  surface  colors  are  of  two  classes. 

1.  Colors  dependent  on  the  chemical  constituents. 

2.  Colors  dependent  on  physical  causes. 

Color  Dependent  on  Chemical  Composition. 

Color  is  one  of  the  least  constant  mineral  characters,  and  varies 
with  different  specimens  of  the  same  species.  It  is  frequently 
changed  by  a  few  hundredths  of  one  per  cent,  of  some  organic  or 
inorganic  substance  dissolved  in  the  mineral,  or  by  larger  amounts 
of  mechanically  included  foreign  material. 

In  describing  color  the  terms  white,  gray,  brown,  black,  blue, 
green,  yellow  and  red  are  used,  with  prefixes,  which  suggest  the 
shade  by  the  color  of  some  familiar  object.  These  need  no  expla- 
nation. 

Color  Due  to  Physical  Causes. 

If  the  observed  surface  color  changes  with  the  direction  in  which 
it  is  viewed  it  is  due  to  interference  of  light. 

Play  or  Change  of  Colors.  —  A  succession  of  colors,  varying  with 
the  direction  the  mineral  is  viewed,  as  in  opal,  labradorite,  or 
diamond. 

Iridescence.  —  Bands  of  prismatic  colors,  either  from  the  interior 
of  a  mineral,  as  from  a  thin  film  of  air  between  cleavages  ;  or  ex- 
ternal and  due  to  a  thin  coating  or  alteration. 

Tarnish.  —  A  surface  which  has  been  exposed  to  the  air  or  to 
moisture  is  often  of  different  color  from  the  fresh  fracture. 

Opalescence.  —  A  milky  or  pearly  reflection,  sometimes  an  effect 
of  crystalline  structure,  at  other  times  due  to  fibrous  inclusions. 

Asterism.  —  A  star  effect  by  reflected  light,  as  in  the  ruby,  or  by 
transmitted  light,  as  in  some  micas,  and  due  to  structure  planes  or 
symmetrically  arranged  inclusions. 

PHOSPHORESCENCE. 

Many  minerals,  after  being  subjected  to  various  outside  influ- 
ences, emit  light  which  often  persists  for  some  time  after  removal 
of  the  exciting  cause.  Such  emission  of  light  is  known  as 
phosphorescence. 


212  MINERALOGY. 

Phosphorescence  may  be  induced  by  ordinary  light,  heat,  fric- 
tion, mechanical  force  or  electrical  stress  but  especially  by  the  action 
of  radium,  polonium  and  actinium  emanations,  by  X-rays  and  by 
ultra-violet  light.  In  a  particular  specimen  it  may  be  induced  by 
only  one  or  by  several  of  the  agencies  named.  Phosphorescence 
is  not  always  a  characteristic  of  species  but  rather  of  the  particular 
specimen  or  of  species  from  a  certain  locality.  On  the  other  hand 
certain  species  are  nearly  always  phosphorescent.  Diamonds  are 
generally  strongly  phosphorescent  under  radium  emanations,  but  the 
degree  of  reaction  varies  with  the  individual  specimen.  They  also 
phosphoresce  under  the  influence  of  polonium,  actinium,  X-rays, 
ultra-violet  rays  and  some  rare  specimens  will  glow  in  the  dark  even 
after  exposure  to  sunlight  or  the  light  of  the  electric  arc.  WilK  mite 
from  Franklin,  New  Jersey,  and  kunzite  are  strongly  phosphor- 
escent under  the  influence  of  radium,  polonium,  actinium  and  X-rays. 
Chlorophane,  a  variety  of  fluorite,  phosphoresces  at  times  by  the 
simple  heat  of  the  hand,  while  fluorite  itself  may  phosphoresce, 
fluoresce  or  do  neither  according  to  the  specimen.  All  minerals  from 
Borax  Lake,  California,  phosphoresce  under  the  influence  of  ultra- 
violet rays,  which  would  seem  to  indicate  some  common  phosphor- 
escent constituent. 

FLUORESCENCE. 

Fluorescence  is  induced  by  much  the  same  agencies  as  phos- 
phorescence, but  the  emitted  light,  which  may  be  white  or  colored, 
persists  only  during  the  action  of  the  exciting  agent.  Colorless 
fluorite  fluoresces  under  the  influence  of  sunlight,  autunite  from 
Mitchell  county,  N.  C.,  and  hyalite  from  San  Luis  Potosi, 
Mexico,  fluoresce  wonderfully  under  the  influence  of  ultra- 
violet light. 

STREAK. 

The  streak  of  a  mineral  is  the  color  of  its  fine  powder.  It  is 
usually  obtained  by  rubbing  the  mineral  on  a  piece  of  hard,  white 
material,  such  as  unglazed  porcelain,  and  brushing  off  the  excess, 
or  it  may  be  obtained  less  perfectly  by  scratching  the  mineral 
with  a  knife  or  file,  or  by  finely  pulverizing  a  fragment  of  the 
specimen. 

The  streak  often  varies  widely  from  the  color  of  the  mass  and  is 
nearly  constant  for  any  species.  When  not  white  it  is  a  character- 
istic very  useful  in  determination. 


PHYSICAL  CHARACTERS.  21$ 

TRANSLUCENCY. 

The  translucency  of  a  mineral  is  its  capacity  to  transmit  light. 

A  mineral  is  said  to  be : 

Transparent.  —  When  objects  can  be  seen  through  it  with  clear- 
ness. 

Subtransparent. — When  objects  can  be  more  or  less  indistinctly 
seen  through  it. 

Translucent. — When  light  passes  through,  as  through  thin  por- 
celain, but  not  enough  to  distinguish  objects. 

Subtranslucent. — When  only  the  thin  edges  show  that  any  light 
passes. 

Opaque. — When  no  light  appears  to  pass  even  through  the 
thin  edges. 

CLEAVAGE   AND    PARTING. 

Many  crystallized  substances  when  sharply  struck  or  when 
pressed  with  a  knife  edge  split  into  fragments  bounded  by  smooth 
plane  surfaces  which  are  always  parallel  to  faces  of  simple  forms* 
in  which  the  substance  can  crystallize. 

These  surfaces  are  more  splintery  than  the  true  crystal  faces 
but  the  angles  between  them  are  just  as  exact  as  the  interfacial 
angles. 

When  the  separation  can  be  obtained  with  equal  ease  in  any  part 
of  the  crystal  and  there  is  only  a  mechanical  limit  to  the  thinness 
of  the  resulting  plates,  the  character  is  called  cleavage.  When, 
however,  the  separation  can  be  obtained  only  at  irregular  intervals 
the  character  is  called  parting.  Furthermore,  all  crystals  of  the 
same  substance  show  the  same  cleavage,  whereas  parting  may  be 
obtained  in  one  crystal  and  not  in  another. 

When  cleavage  or  parting  is  obtained  parallel  to  one  face  of  a 
crystal  form  it  will  be  obtained  with  equal  ease  parallel  to  all  faces 
of  the  form.  For  instance,  galenite  cleaves  parallel  to  all  planes 
of  the  cube,  Fig.  275  ;  calcite,  Fig.  276,  in  three  directions  parallel 
to  all  the  faces  of  a  rhombohedron  with  diedral  angles  of  105°  5'  ; 
and  some  crystals  of  hematite  show  parting  planes  parallel  to  all 
the  faces  of  the  rhombohedron. 

Cleavage  may  be  obtained  parallel  to  the  faces  of  two  or  more 
crystal  forms,  for  instance  gypsum  splits  easily  into  plates  parallel 
to  the  clino-pinacoid,  these  plates  again  break  parallel  to  the  ortho- 


214 


MINERALOGY. 


pinacoid  and  to  the  dome  { i  o  I }  and  the  final  shape  is  a  rhombic 
plate  with  angles  of  66°. 

Terms  of  Cleavage.  —  Cleavage  is  said  to  be  perfect  or  eminent 
when  obtained  easily,  giving  smooth,  lustrous  surfaces.      Inferior 

FIG.  298. 


Galenite  Cleavage,  Pyrenees,  alter  Lacroix. 

degrees  of  ease  of  cleavage  are  called  distinct,  indistinct  or  imper- 
fect, interrupted,  in  traces,  difficult. 

Manipulation.  —  Directions  of  cleavage  are  often  indicated  by  a 
pearly  lustre  on  faces  parallel  to  the  cleavage  direction,  the  lustre 
being  due  to  repeated  light  reflections  from  cleavage  rifts,  or 

FIG.  299. 


Calcite  Cleavage. 

cracks  may  be  visible.  The  absence  of  indications  is  not  proof 
that  cleavage  cannot  be  obtained,  but  only  that  previous  pressure 
or  shock  have  not  started  the  separation. 


PHYSICAL   CHARACTERS. 


215 


Cleavage  is  usually  obtained  by  placing  the  edge  of  a  knife  or 
small  chisel  upon  the  mineral  parallel  to  the  supposed  direction  of 
cleavage  and  striking  a  quick,  sharp  blow  upon  it  with  a  hammer. 
In  some  instances  the  cleavage  is  produced  by  heating  and  sud- 
denly plunging  the  mineral  in  cold  water.  Sudden  heat  alone  will 
often  produce  decrepitation  and  with  easily  cleavable  minerals  the 
fragments  will  be  cleavage  forms. 

Frequently  the  cleavage  is  made  apparent  during  the  grinding 
of  a  thin  section. 

Parting  is  a  secondary  character  produced  in  some  instances  and 
not  in  others  as  a  result  of  pressure  after  solidification.  It  takes 
place  along  a  so-called  glide  plane.* 

PERCUSSION   FIGURES. 

If  a  rod  with  a  slightly  rounded  point  is  pressed  against  a  firmly 
supported  plate  of  mica  and  tapped  with  a  light  hammer,  three 
little  cracks  will  form,  radiating  f  from  the  point, 
Fig.  301.      The  most  distinct  of  these  is  always  FIG.  301. 

parallel  to  the  clino-pinacoid,  the  others  at  an 
angle  ;r  thereto  which  is  53°  to  56°  in  muscovite, 
59°  in  lepidolite,  60°  in  biotite,  61°  to  63°  for 
phlogopite. 

In  the  same  way  on  cube  faces  of  halite  a 
cross  is  developed  with  arms  parallel  to  the  diag- 
onals of  the  face.  On  an  octahedral  face  a 
three-rayed  star  is  developed. 

ELASTICITY. 

Elasticity  is  capable  of  exact  measurement,  but  is  of  little  value 
in  determination  of  minerals.  The  following  terms  are  used  : 

Elastic. — A  thin  plate  will  bend  and  then  spring  back  to  its 
original  position  when  the  bending  force  is  removed,  as  in  mica. 

Flexible  or  Pliable. — A  thin  plate  will  bend  without  breaking, 
as  in  foliated  talc. 

*The  artificial  development  of  a  glide  plane  fgbm  in  calcite  is  shown  in  Fig.  300. 

If  the  edge  ad  of  the  larger  angle  is  rested  upon  a  steady  support  and  the  blade  of  a 
knife  pressed  steadily  at  some  point  i  of  the  opposite  edge,  the  portion  of  the  crystal 
between  i  and  c  will  be  slowly  pushed  into  a  new  position  of  equilibrium  as  if  by  rota- 
tion about  fgbm  until  the  new  face  gcfb  and  the  old  face  gcb  make  equal  angles  with 
fgbm. 

f  By  pressure  alone,  three  cracks  diagonal  to  these  are  developed. 


2l6  MINERALOGY. 

TENACITY. 

The  following  terms  are  used : 

Brittle.  —  Breaks  to  powder  before  a  knife  or  hammer  and  can- 
not be  shaved  off  in  slices. 

Sectile.  —  Small  slices  can  be  shaved  off  which,  however,  crumble 
when  hammered. 

Malleable. — Slices  can  be  shaved  off  which  will  flatten  under 
the  hammer. 

Tough.  —  The  resistance  to  tearing  apart  under  a  strain  or  a 
blow  is  great. 

Ductile. —  Can  be  drawn  into  wire.  Every  ductile  mineral  is 
malleable  and  both  are  sectile. 

The  sectile  minerals  are:  graphite,  bismuth,  copper,  silver, 
gold,  platinum,  chalcocite,  agentite,  molybdenite,  orpiment,  tetra- 
dymite,  senarmontite,  arsenolite,  cerargyrite. 

FRACTURE. 

When  the  surface  obtained  by  breaking  is  not  a  plane  or  a  step- 
like  aggregation  of  planes  it  is  called  a  fracture  and  described  as  : 

Conchoidal,  rounded  and  curved  like  a 

"pip      •302  1       11       T~>« 

*  shell,  rig.  302. 

Even,  approximately  plane. 

Uneven,  rough  and  irregular. 

Hackly,  with  jagged  sharp  joints  and 
depressions  as  with  metals. 

Splintery,  with  partially  separated  splin- 
ters or  fibers. 

HARDNESS. 

The  resistance  of  a  smooth  plane  surface  to  abrasion  is  called  its 
hardness,  and  is  commonly  recorded*  in  terms  of  a  scale  of  ten 
common  minerals  selected  by  Mohs: 

*  In  more  exact  testing  the  crystal  may  be  moved  on  a  little  carriage  under  a  fixed 
vertical  cutting  point  and  the  pressure  determined,  which  is  necessary  to  produce  a  vis- 
ible scratch.  Other  methods  are  planing  or  boring  with  a  diamond  splinter  under  con- 
stant pressure,  and  comparing  the  loss  in  weight  for  a  given  penetration  or  given  num- 
ber of  movements.  The  loss  of  weight  during  grinding  and  the  pressure  necessary  to 
produce  a  permanent  indentation  or  a  crack  have  also  been  used  as  determinants  of 
hardness.' 


PHYSICAL   CHARACTERS.  21 7 

1.  Talc,  laminated.  6.    Orthoclase,  white  cleavable. 

2.  Gypsum,  crystallized.  7.    Quartz,  transparent. 

3.  Calcite,  transparent.  8.    Topaz,  transparent. 

4.  Fluorite,  crystalline.  9.   Sapphire,  cleavable. 

5.  Apatite,  transparent.  10.  Diamond. 
Intermediate  values  are:  Window  glass  5.5,  Jewelers  file  6.5, 

Zircon  7.5,  Chrysoberyl  8.5,  Carborundum  9.5. 

These  numbers  have  no  quantitative  relation — there  is  no  com- 
mon difference.  The  diamond  is  much  further  from  sapphire  than 
this  is  from  talc.* 

In  testing,  some  inconspicuous  but  smooth  surface  of  the  mineral 
is  selected  and  a  sharp  point  of  known  hardness  is  pressed  upon  the 
surface  and  moved  back  and  forth  several  times  on  the  same  line  a 
short  distance  (y&  inch}.  If  the  mineral  is  not  scratched  it  is 
harder  than  the  standard  used,  and  the  next  higher  on  the  scale  is 
tried  in  the  same  way. 

A  good  method  is  to  try  the  hardness  of  the  mineral  first  with 
the  finger  nail  (2.5),  then  with  a  pocket  knife  (about  6). 

(a)  If  the  finger  nail  cuts  then  2  and  I  are  tried. 

(ft)  If  the  finger  nail  makes  no  scratch  but  the  knife  does  3,4,  5, 
and  6  are  tried. 

(c)  If  the  knife  does  not  scratch  the  specimen  the  harder  mem- 
bers, 6  to  10,  are  used  successively  until  one  is  found  which 
scratches  the  mineral. 

The  jewelers  file  and  conical  pencils  made  of  the  upper  members 
of  the  scale  are  much  used. 

For  cut  stones  and  other  valuable  specimens  it  is  often  wise  to 
use  dully  polished  slabs  of  the  test  minerals  and  determine  the 
power  of  an  edge  of  the  cut  stone  to  scratch  the  polished  test 
piece. 

Care  must  be  taken  to  distinguish  between  a  true  scratch  and 
the  production  of  a  "  chalk  "  mark  which  rubs  off.  Altered  or 
rough  surfaces  must  be  avoided. 

Pulverulent  fibrous  or  splintery  minerals  are  "  broken  down  " 
or  their  particles  pushed  aside  by  the  test  and  yield  an  "apparent" 
hardness  often  much  lower  than  the  true  hardness. 

*  The  average  of  five  attempted  comparisons  from  9  down  give  roughly  sapphire 
100,  topaz  30,  quartz  18,  orthoclase  12,  apatite  7,  fluorite  3^,  calcite  2^,  gypsum  %. 


218 


MINERALOGY. 


ETCHING   FIGURES     . 

When  a  crystal  or  cleavage  is  attacked  by  any  solvent  the  action 
proceeds  with  different  velocities  in  crystallographically  different 
directions,  and  if  stopped  before  the  solution  has  proceeded  far,  the 
crystal  faces  are  often  pitted  with  little  cavities  of  definite  shape. 

The  absolute  shape  varies  with  many  conditions  ;  time,  tempera- 
ture, solvent,  crystallographic  orientation  and  chemical  composition. 

The  figures,  whatever  their  shape,  conform  in  symmetry  to  the 
class  to  which  the  crystal  belongs,  and  are  rarely  forms  common 
to  several  classes.  They  are  alike  on  faces  of  the  same  crystal 
form  and  generally  unlike  on  faces  of  different  forms,  and  serve, 
therefore,  as  an  important  means  (perhaps  the  most  important)  for 
determining  the  true  grade  of  symmetry  of  a  crystal  and  also  for 
recognizing  and  distinguishing  faces. 

Fig.  303  shows  the  shape  and  direction  of  the  etchings  upon  a 
cube  of  pyrite.  These  conform  to  the  symmetiy  of  the  group  01 


FIG.  303. 


FIG.  304. 


«» 

*• 


the  diploid,  p.  65.  On  the  other  hand  the  etchings  upon  a  cube 
of  fluorite,  Fig.  304,  show  a  higher  symmetry  corresponding  to 
that  of  the  hexoctahedral  group,  p.  58. 

SPECIFIC   GRAVITY. 

.  The  specific  gravity  of  a  substance  is  equal  to  its  weight  divided 
by  the  weight  of  an  equal  volume  of  distilled  water.  The  character 
is  an  unusually  constant  one,  the  variations  in  varieties  of  the  same 
species  not  being  great  and  even  these  being  due  usually  to  actual 
differences  in  composition. 

Strictly  the  temperature  of  the  water  should  be  4°  C.,  or  if  not  the  result  should  be 
multiplied  by  a  factor  which  is  the  specific  gravity  of  the  water  used.  Generally  the 
water  is  used  at  the  ordinary  room  temperature  without  correction. 


PHYSICAL    CHARACTERS. 


2I9 


Pure  material  must  be  selected  free  from  cavities,  and  air  bubbles 
clinging  to  the  surface  must  be  brushed  off  while  the  fragment  is  in 
the  water. 

Substances  soluble  in  water  must  be  determined  in  alcohol, 
benzine  or  other  liquids  in  which  they  are  insoluble,  and  the  result 
multiplied  by  the  specific  gravity  of  the  liquid  used. 

The  specific  gravities  of  the  minerals  considered  in  this  book 
range  from  water  (ice)  0.92,  to  iridosmine  19  to  21. 

Minerals  of  metallic  and  submetallic  luster  are  heavy,  rarely  as 
low  as  4.  The  great  group  of  silicates  range  chiefly  between 
2  and  3.5,  zircon  reaching  4.7. 

Direct  Weighing  in  a  Delicate  Balance. 

Except  for  very  small  material  the  most  accurate  results  are 
obtained  with  a  delicate  balance  such  as  an  assay  balance  or  a  dia- 
mond balance,  Fig.  305,  within  at  least  one  tenth  milligram.  The 

FIG.  305. 


result  should  be  correct  to  the  third  decimal.  A  small  wooden 
bench,  Fig.  306,  is  used  to  hold  a  beaker  of  distilled  water  above 
the  scale  pan,  and  a  platinum  spiral,  Fig.  307,  to  hold  the  stone. 
Three  weighings  are  needed  : 

W=  weight  of  the  stone. 

S=  weight  of  the  spiral  when  suspended  from  the  end  of  the 


22O 


MINERALOGY. 


determined  balance  frame  and  immersed  in  the  distilled  water  as 
in  Fig.  307.     (This  weight  may  be  made  once  for  all.) 

W  =  weight  of  the  stone  and  the  spiral  suspended  in  distilled 

water. 

W 
Then,  Sp.  Gr.  =  5+  w_  w  - 

Usually  no  correction  need  be  made  for  temperature.* 

The  Jolly  Balance. 

This  instrument  gives  the  relative  weights  in  terms  of  the 
stretching  of  a  spiral  spring.  In  the  older  form,  Fig.  308,  two 
scale  pans  c  and  d  are  attached,  one  below  the  other,  to  a  spiral 
spring  parallel  to  which  is  a  mirror  with  a  graduated  scale. 

FIG.  308. 


FIG.  307. 


FIG.  306. 


The  lower  pan  d  is  kept  submerged  in  distilled  water.  Three 
readings  are  made  by  noting  the  heights  at  which  the  white  bead 
b  on  the  wire  and  its  image  in  the  graduated  mirror  coincide  when 
the  spiral  comes  to  rest. 

*  Greater  speed  and,  if  proper  corrections  for  temperature  are  made,  equal  or 
greater  accuracy  are  obtained  by  substituting  for  distilled  water  benzol  or  toluol,  which 
have  less  surface  tension  than  water.  The  result  obtained  by  the  above  formula  must 
then  be  multiplied  by  the  specific  gravity  of  the  benzol  or  toluol  for  the  temperature  at 
which  the  weighing  was  made. 


PHYSICAL    CHARACTERS. 


221 


A.  Instrument  reading  with  nothing  in  either  scale  pan. 

B.  Reading  with  mineral  in  upper  scale  pan. 

C.  Reading  with  same  fragment  transferred  to  lower  scale  pan. 

B-A 
Sp.  Gr.  =  w-—c 

The  result  is  quickly  attained  and  unless  the  fragment  is  small 
is  accurate  to  the  second  decimal. 
The  Kraus  Recording  Jolly  Balance. 

Professor  Kraus  described*  an  improved  Jolly  balance,  Fig. 


FIG.  309. 


FIG.  310. 


W 


•20- 


Z2- 


309,  requiring  only  two  readings,  which  may  be  verified  at  the  end 
of  the  operation. 

*  Described  in  Am.  Jour  Sci.,  XXXI,  561,  1911       Made  by  Eberbach  &  Son  Com- 
pany, Ann  Arbor,  Mich. 


222  MINERALOGY. 

The  parts  are  :  (The  scale  and  verniers  are  shown  enlarged, 
Fig.  310). 

(a)  An  outer  rectangular  tube  with  a  fixed  vernier,  W. 

(ft)  An  inner  round  tube  movable  by  a  milled  head  and  carrying 
with  it  a  second  vernier,  L. 

(c)  An  adjustable  rod  within  the  round  tube,  carrying  the  spring 
and  scale  pans  and  a  pointer  which  swings  in  front  of  a  small  cir- 
cular mirror. 

(d*)  A  graduated  scale  which  may  be  clamped,  or  if  undamped 
moves  with  the  inner  tube. 

The  operation  is  as  follows  : 

1.  The  graduated  scale,  the  two  verniers  and  the  pointer  are  all 
placed  at  zero,  the  lower  scale  pan  being  immersed  in  water. 

2.  The  fragment  is  placed  in  the  upper  scale  pan,  the  scale  un- 
damped and  the  milled  head  turned,  driving  the  round  tube  and 
its  attachments  upward  until  the  pointer  is  again  at  zero.     The 
reading  of  W  corresponds  to  the  weight  in  air. 

3.  The  fragment  is  transferred  to  the  lower  scale  pan,  the  scale 
clamped,  the  milled  head  turned  till  the  pointer  is  again  at  zero. 
The  reading  of  L  corresponds  to  the  loss  of  weight  in  water. 
Hence, 

c      r  W 

Sp.  Gr.  =  -j-  . 

A  minor  advantage  is  that  both  weighings  remain  recorded  until 
the  end  of  the  operation  and  may  be  checked. 

Method  for  Small  Fragments. 

The  difficulty  of  determining  small  grains  by  the  chemical  bal- 
ance lies  in  the  weighing  in  water  rather'  than  the  weighing  in  air. 
The  following  simple  method  *  has  been  used:  Substitute  for  the 
spiral  a  small  vessel  containing  vaseline.  Weigh  this  in  air  and 
water,  denoting  these  weights  by  w  and  wr  .  Place  several  of  the 
little  crystals  or  grains  on  the  vaseline  and  weigh  in  air,  denoting 
this  by  W,  then  warm  the  vaseline  and  let  them  sink  into  it  and 
weigh  in  water,  denoting  this  by  W  y  then 

q  W-w 

~ 


R.  Smeeth,  Sci.  Proc.  Roy.  Dublin  Soc.,  6,  1888,  61. 


PHYSICAL    CHARACTERS.  223 

Using  the  Pycnometer  or  Specific  Gravity  Flask. 

Very  porous  minerals  and  powders  are  determined  by  weighing 
in  a  little  glass  bottle  the  stopper  of  which  ends  in  a  fine  tube.  In 
a  later  form  there  are  two  openings,  one,  the  neck,  is  closed  by  a 
ground  stopper  carrying  a  thermometer,  the  other  ends  in  a  capil- 
lary tube. 

In  ordinary  use  the  mineral  is  weighed  (A)  and  the  bottle  full 
of  water  is  also  weighed  {B\  The  mineral  is  then  inserted  in  the 
bottle  and  displaces  its  bulk  of  water,  and  the  difference  between 
this  weight  ( C)  and  the  sum  of  the  other  two  weights  is  the  weight 
of  the  displaced  water. 

c     r  A 

Sp.Gr.  =  £  +  A_c. 

If  special  precautions  *  are  used  this  apparatus  may  be  relied 
upon  to  the  third  decimal  with  one  gram  of  substance. 

Complete  removal  of  air  bubbles  is  secured  by  placing  the  pycnometer  under  an  air 
pump  after  the  fragments  are  covered  with  the  liquid. 

Using  Heavy  Liquids. 

If  a  fragment  of  a  mineral,  which  may  be  very  minute,  is  dropped 
into  a  test-tube  containing  a  liquid  of  higher  specific  gravity  it  will 
float.  If  the  liquid  is  diluted,  the  diluent  being  stirred  in  drop  by 
drop,  there  will  be  one  stage  at  which  the  fragment  if  pushed  down 
will  neither  sink  nor  rise  but  stay  where  pushed. 

The  specific  gravity  of  the  liquid  is  then  determined  either 
roughly  by  dropping  in  fragments  of  material  of  known  specific 
gravity  until  one  is  found  which  just  sinks  and  another  which 
floats,  the  liquid  being  of  a  specific  gravity  between  these  ;  or  for 
more  accurate  determination  the  most  convenient  balance  is  that 
of  Westphal,  Fig.  285.  The  beam  is  graduated  in  tenths  and 
the  weights  A,  B  and  C  are  respectively  unit,  -^  and  -j-J-^. 

This  balance  is  so  constructed  that  when  the  thermometer  float 
is  suspended  in  distilled  water  at  15°  C.  a  unit  weight  must  be 
hung  at  the  hook  to  obtain  equilibrium. 

If  then  the  test-tube  is  nearly  filled  with  the  heavy  liquid  and 
weights  added  until  equilibrium  is  secured  the  specific  gravity  is 
known. 

*  See  Mier's  Mineralogy,  p.  191. 

f  For  the  use  of  heavy  liquids  in  preparation  of  material  for  Chemical  Analyses  see 
Iddings,  Rock  Minerals,  p.  25. 


224 


MINERALOGY. 


For  instance  in  the  figure  the  weights  employed  are : 

Unit  weight  at  hook,  value i.ooo 

Unit  weight  at  sixth  division,  value 0.600 

JQ  weight  at  sixth  division,  value 0.060 

weight  at  ninth  division,  value 0.009 


Specific  gravity  .  . 1.669 


The  Westphal  Balance. 

The  principal  heavy  liquids  are  :  * 

Thoulet  Solution.  —  Mercuric  iodide  and  potassium  iodide,  in  the 
ratio  of  five  parts  to  four  by  weight,  are  heated  with  a  little  water 
until  a  crystalline  scum  forms,  then  filtered.  The  maximum  spe- 
cific gravity  is  nearly  3.1  and  may  be  lowered  by  the  addition  of 
water  to  any  desired  value. 

Klein  Solution. — Cadmium  borotungstate  with  a  maximum  spe- 
cific gravity  of  3.6  if  fused,  3.3  if  dissolved. 

Brauris  Solution. — Methylene  iodide,  CH2T2,  with  a  maximum 
specific  gravity  of  3.32  which  can  be  lowered  by  the  addition  of 
benzol.  It  darkens  from  exposure  to  light  but  may  be  clarified 
by  shaking  with  a  little  mercury  or  copper. 

By  addition  of  iodoform  and  iodine  it  may  be  raised  to  a  specific 
gravity  of  3.65. 

*See  Neues  Jahrb.  f.  Min.,  1889,  II.,  185,  for  list  of  solids  which  when  melted 
have  specific  gravity  up  to  5. 


PHYSICAL   CHARACTERS.  225 

Retger's  Solution. — Silver  thallium  nitrate  which  is  liquid  at  75° 
C,  has  a  maximum  specific  gravity  of  over  4.5  which  can  be  low- 
ered by  the  addition  of  hot  water. 

Specific  Gravity  Tubes. 

In  gem  testing,  a  series  of  tubes,  usually  three,  fitted  with  glass 
stoppers  or  corks  and  containing  liquids  of  different  densities  are 
sometimes  used  and  by  diluting  and  using  "  indicators,"  that  is, 
fragments  of  a  known  specific  gravity,  the  gravity  of  a  liquid  which 
just  floats  a  specimen  may  be  tested. 

Diffusion  Columns. 

By  pouring  into  a  test  tube  a  heavy  liquid  and  on  top  of  this  a 
lighter  liquid  and  allowing  these  to  stand  several  hours  a  diffusion 
takes  place  so  that  the  density  increases  regularly  with  the  depth. 
By  use  of  "indicators"  the  Sp.  Gr.  for  the  level  to  which  the 
stone  sinks  may  be  determined.* 

TASTE. 

Minerals  soluble  in  water  often  have  a  decided  taste : 

Astringent.  —  The  taste  of  alum. 

Saline  or  Salty.  —  The  taste  of  common  salt. 

Bitter.  —  The  taste  of  epsom  salts. 

Alkaline.  —  The  taste  of  soda. 

Acid.  —  The  taste  of  sulphuric  acid. 

Cooling.  —  The  taste  of  nitre. 

Pungent.  —  The  taste  of  sal-ammoniac. 

ODOR. 

Odors  are  rarely  obtained  from  minerals,  except  by  setting  free 
some  volatile  constituent.  The  terms  most  used  are  : 

Garlic.  — The  odor  of  garlic  obtained  by  heating  minerals  con- 
taining arsenic. 

Horseradish.  —  The  odor  of  decayed  horseradish  obtained  from 
minerals  containing  selenium. 

Sulphurous.  —  The  odor  obtained  by  heating  sulphur  or  suL 
phides. 

Fetid.  —  The  odor  obtained  by  dissolving  sulphides  in  acid. 

Bituminous.  —  The  odor  of  bitumen. 

*See  Mier's  Mineralogy,  p.  192. 
16 


226  MINERALOG  Y. 

Argillaceous.  —  Obtained  from  serpentine  and  some  allied  min- 
erals, after  moistening  with  the  breath. 

FEEL. 

Terms  indicating  the  sense  of  touch  are  sometimes  used : 

Smooth.  —  Like  celadonite  or  sepiolite. 

Soapy.  —  Like  talc. 

Harsh  or  Meager.  —  Like  aluminite. 

Cold.  —  Distinguishes  gems  from  glass. 

THE    THERMAL   CHARACTERS. 

Transmission  of  Heat  Rays. 

HEAT  rays  may  be  reflected,  refracted,  doubly  refracted,  polar- 
ized and  absorbed,  and  it  is  possible,  though  difficult,  to  determine 
a  series  of  thermal  constants  for  crystals. 

Conductivity. 

The  rapidity  with  which  heat  is  conducted  in  different  directions 
in  a  crystal  is  in  accordance  with  its  symmetry.  This  may  be 
shown  on  any  face  or  cleavage  surface  as  follows: 

(a)  The  surface  is  breathed  upon,  quickly  touched  by  a  very  hot  wire,  dusted  with 
lycopodium  powder,  turned  upside  down  and  tapped  carefully.  The  powder  falls  from 
where  the  moisture  film  has  evaporated,  but  adheres  elsewhere,  giving  a  sharply  out- 
lined figure.  The  entire  operation  should  take  less  than  three  seconds. 

(<5)  The  surface  is  coated  with  a  mixture  of  three  parts  elaidic  acid  and  one  part 
wax,  brought  into  contact  with  a  hot  wire,  and  the  temperature  maintained  until  the  wax 
has  meked  around  the  wire.  The  boundary  of  the  melted  patch  is  visible,  after  cool- 
ing, as  a  ridge. 

A  circle  indicates  either  an  isometric  crystal  or  a  basal  section 
of  a  hexagonal  or  tetragonal  crystal.     All  other  sections  yield 
ellipses  varying  in  eccentricity  and  in  position  of  axes. 
Expansion. 

When  a  crystal  is  uniformly  heated,  directions  crystallographic- 
ally  alike  expand  in  the  same  proportion,  but  directions  unlike 
do  not 

The  expansion  may  be  accurately  measured  for  any  direction 
but  the  methods  involve  apparatus  of  great  precision  and  cost. 
Change  of  Crystal  Angles  Produced  by  Expansion. 

An  isometric  crystal  uniformly  heated  expands  without  change 
of  angles.  In  all  other  systems  the  expansion  varies  with  the 
direction  and  certain  angles  are  changed 


PHYSICAL    CHARACTERS.  227 

THE  MAGNETIC  CHARACTERS. 

Magnetism.  —  A  few  iron-bearing  minerals  attract  the  magnetic 
needle  or  are  attracted  by  a  steel  magnet.  Of  these  minerals, 
magnetite,  pyrrhotite  and  platinum  will  themselves  occasionally 
act  as  magnets. 

Para-  and  Diamagnetism. 

Any  substances  will  be  either  attracted  or  repelled  in  some 
degree  in  the  field  of  a  strong  electromagnet. 

If  a  rod  of  the  substance  is  suspended  by  a  fiber  so  as  to  swing  horizontally  between 
the  poles  of  an  electromagnet,  the  rod  is  paramagnetic,  if  pulled  into  "axial"  posi- 
tion with  its  ends  as  near  the  poles  of  the  magnet  as  possible,  and,  is  diamagnetic,  if 
pushed  into  an  "equatorial"  position  with  its  ends  as  far  from  the  magnetic  poles  as 
possible. 

Crystals  are  more  strongly  magnetized  in  certain  directions  than  in  others. 

Action  on  a  Magnetic  Needle.    Haiiy's  Method  of  Double  Magnetism. 

A  delicate  magnetic  needle,  or  as  Hau'y  showed,  a  needle  made 
by  a  bar  magnet  to  take  an  east  and  west  position,  may  be  attracted 
by  stones  containing  iron,  such  as  garnet,  chrysolite,  tourmaline. 

ELECTRICAL  CHARACTERS. 

Heat,  friction  and  pressure  often  develop  electric  charges  in 
minerals.  The  charges  are,  however,  weak  and  the  chief  differ- 
ences lie  in  the  length  of  time  the  electricity  is  retained. 

In  the  testing  the  drier  the  atmosphere,  the  better.  If  humidity 
is  great  no  results  may  be  obtained.  The  best  results  are  obtained 
from  polished  surfaces. 

In  handling  the  material  an  insulated  pincers  would  be  better 
than  the  fingers. 

Frictional  Electricity. 

All  minerals  are  electrified  by  friction  but  the  -f  or  —  character 
may  vary  in  varieties  of  a  species  and  even  in  the  same  specimen. 

The  electricity  is  developed  by  brushing  or  striking  several  with 
a  woolen  cloth.  Its  presence  is  recognized  by  taking  a  stone  by 
an  insulated  holder  near  some  form  of  electrometer. 

The  duration  of  the  charge  is  determined  by  placing  the  min- 
eral stone  in  contact  with  a  metal  plate  which  is  itself  in  contact 
with  surrounding  bodies,  and  in  a  dry  room.  From  time  to  time 
the  mineral  is  again  tried  with  the  electrometer. 


228  MINERALOGY, 

Although  Haliy  devoted  considerable  space  *  to  these  properties 
they  have  not  been  developed  much  since  his  day. 

Haiiy  used  a  light  brass  rod  with  brass  spheres  on  both  ends,  balanced  like  a 
magnetic  needle  on  a  fine  point.  This  being  electrified,  either  positively  by  bringing 
near  a  rod  of  electrified  sealing  wax,  or  negatively  by  touching  with  the  rod,  an  elec- 
trified mineral  will  attract  or  repel  the  needle  according  as  it  has  opposite  or  similar 
electricity. 

Similarly  a  pith  ball  suspended  by  a  silk  thread  may  be  charged  and  used  or  cat's 
hair  may  be  positively  electrified  by  rubbing  between  the  fingers. 

The  Bohnenberger-Fechner  Electrometer  is  a  more  elaborate  device  consisting  of  a 
single  gold  leaf,  hanging  between  poles  of  a  Zamboni  dry  battery      The  stone  is  ap 
preached  to  the  knob  on  the  conductor.     If  the  stone  was  electrified,  the  gold  leaf 
becomes  charged  and  clings  to  the  opposite  pole  of  the  battery. 

The  following  examples  illustrate  the  property  : 
Electrified  Positively  by  Friction. 

Topaz,  24  hours  duration.  Rock  crystal,  J^  hour. 

Corundum,  several  hours  duration.         lolite,  ^  hour. 

Odontolite,  several  hours  duration.         Diamond,  y2  hour. 
Also  spinel,  tourmaline,  garnet,  chrysolite,  beryl,  spodumene,  zir- 
con, moonstone,  axinite,  titanite,  phenacite,  diopside,  epidote. 

Sulphur  and  amber  are  examples  of  minerals  which  develop 
negative  electricity. 

Electrical  Conductivity. 

All  minerals  conduct,  but  practically,  conductivity  is  limited  to 
the  metals,  some  metalloids,  most  sulphides,  tellurides,  selenides, 
bismuthides,  arsenides  and  antimonides,  some  of  the  oxides,  and, 
at  higher  temperature,  a  few  haloids. 

If  a  rod  is  introduced  into  a  weak  current,  the  strength  of  which  is  varied  by  resist- 
ances and  the  deviation  observed  in  a  galvanometer,  the  results  will  vary  for  different 
minerals  between  very  wide  limits  dependent  upon  the  constitution  of  the  chemical 
molecule  more  than  upon  the  crystalline  structure. 

Practical  applications  of  this  property  are  the  electrostatic  con- 
centrators in  which  the  mixture  falling  on  a  moving  surface  is 
electrified  more  or  less  rapidly  according  to  its  conductivity  and 
thereby  (repelled)  different  distances. 

Similarly  a  flat  stick  of  sealing  wax  made  electric  by  rubbing 
and  held  over  a  fine  sand-like  mixture  will  attract  the  better  con- 
ductors ;  for  example,  will  take  cassiterite  from  zircon. 

*  Traite  des  caracteres  physiques  des  Pierres  Precieuses,  Paris,  1817,  pp.  113-185. 


PHYSICAL  CHARACTERS.  229 

These  changes  may  be  measured  with  accurate  goniometers  and 
the  relative  expansions  calculated. 

Change  of  Optical  Characters  Produced  by  Expansion. 

The  expansion  of  a  crystal  changes  the  indices  of  refraction  for 
different  directions.  With  isometric  crystals  the  index  may  become 
either  larger  or  smaller.  With  tetragonal  and  hexagonal  crystals 
the  principal  indices  of  refraction  may  alter  unequally.  The  inter- 
ference figure  will  also  alter  and  for  a  particular  temperature  will 
disappear. 

In  orthorhombic,  monoclinic  and  triclinic  crystals  the  interference 
figure  may  undergo  even  more  striking  changes.  For  instance, 
in  gypsum  with  yellow  light  at  20°  C.  the  axial  angle  is  92°,  at 
100°  C.  it  is  reduced  to  51°,  at  134°  C.  it  is  zero,  and  for  still 
higher  temperatures  the  optic  axes  pass  into  a  plane  at  right  angles 
to  their  former  position. 

Melting  and  Inversion  Points. 

Fusibility  in  terms  of  a  rough  scale  as  a  blowpipe  test  has  been 
described,  p.  164,  and  changes  of  color  and  other  phenomena  by 
moderate  heat  on  p.  1 76. 

Recent  improvements  in  the  thermoelectric  couple  and  the 
electric  resistance  furnace  have  made  possible  laboratory  deter- 
minations of  the  changes  which  minerals  undergo  with  increased 
temperatures  and  the  consequent  changes  in  volume,  etc.,  are  01 
great  geological  importance.  Both  the  melting  point,  that  is  "  the 
temperature  at  which  the  crystalline  and  the  liquid  substance  can 
remain  side  by  side  in  equilibrium  "  and  the  inversion  point,  that 
is  "  the  temperature  at  which  two  different  crystalline  forms  of  the 
same  substance  can  so  remain  are  determined." 

For  instance  a  quartz  changes  to  /3  quartz  at  575°  C.  and  to  christobaltite  at  about 
800°,  and  the  latter  melts  at  about  1600°  C.  Similarly  anorthite  melts  at  1552°, 
albite  below  1200°,  and  their  isomorphous  mixtures  at  intermediate  values. 

The  presence  of  other  minerals  lowers  the  melting  point  and 
pure  types,  usually  synthetic,  are  used.  Natural  minerals  usually 
show  a  "  melting  interval  "  of  40  or  50  degrees.* 

*See  publications  of  Dolter,  Neues  Jahrb.  f.  Min.,  u,  60,  1903.  Tschermak, 
Min.  Mitt.,  21,  211,  307.  Also  Joly,  Trans.  Roy.  Dublin  Soc.,  6,  283,  and  the  more  recent 
work  of  Day,  White,  Sosman  and  others,  in  the  Geophysical  Laboratory  publications. 


230  MINERALOGY. 

Pyroelectricity  and  Piezoelectricity. 

Poorly  conducting  crystals  which  have  not  a  center  of  symmetry 
if  altered  in  volume  either  by  a  temperature  change  or  by  pressure 
will  frequently  accumulate  positive  and  negative  charges  of  elec- 
tricity at  different  points. 

PYROELECTRICITY.  —  Usually  the  crystal  is  heated  in  an  air- 
bath  to  a  uniform  temperature,  then  drawn  quickly  once  or  twice 
through  an  alcohol  flame  and  allowed  to  cool.  During  the  cooling 
of  the  crystal  positive  charges  collect  at  the  so-called  antilogue 
poles,  and  the  negative  charges  at  the  analogue  poles. 

In  PIEZOELECTRICITY  the  charges  are  developed  by  pressure,  for 
instance,  calcite  pressed  between  the  fingers  becomes  positively 
electrified,  tourmaline  compressed  in  the  direction  of  the  vertical 
axis  develops  a  positive  charge  at  the  antilogue  end  and  a  negative 
charge  at  the  analogue  end  or  precisely  the  charges  which  would 
result  from  cooling  a  heated  crystal. 

The  charges  are  detected  by  such  methods  as  are  described 
under  frictional  electricity. 

In  Kundfs  Method  the  positive  and  negative  poles  may  be  distinguished  by  blow- 
ing upon  the  cooling  crystal  a  fine  well  dried  mixture  of  equal  parts  of  powdered 
sulphur  and  red  oxide  of  lead;  The  nozzle  of  the  bellows  is  covered  by  a  fine  muslin 
net.  In  passing  through  the  sieve,  the  sulphur  is  negatively  electrified  and  is  attracted 
by  the  antilogue  poles,  coloring  them  yellow,  while  the  minimum  is  positively  electri- 
fied and  is  caught  by  the  analogue  poles,  coloring  them  red. 


CHAPTER  XVI. 

i 

CHEMICAL   CHARACTERS   OF   MINERALS. 

Minerals  are  either  elements  or  are  formed  by  the  uniting  of 
atoms  of  different  elements  in  definite  proportions  in  accord- 
ance with  the  laws  of  chemistry  and  for  either  identification  or 
classification  their  chemical  composition  is  their  most  important 
characteristic. 

Empirical  Formulas. 

The  chemical  composition  of  a  mineral  is  determined  by  exact 
quantitative  analysis  and  from  this  a  formula  is  calculated  which 
shows  which  elements  and  how  many  atoms  of  each  occur  therein. 
Such  formulas  are  called  empirical  and  do  not  of  necessity  express 
the  structure  of  the  molecule,*  but  only  the  composition  ratio. 
In  fact,  the  symbols  adopted  are  always  the  simplest  which  can 
express  the  proportions  shown  by  analysis  to  exist  between  the 
atoms  and  which  satisfy  their  valences. 

Calculation  of  Formulas. 

A  very  pure  specimen  of  beryl  gave  the  following  results  on 

analysis: 

Per  cent 

BeO, 14.01 

A1203, 19.26 

Si02, 66.3; 

The  sum  of  the  atomic  weights  for  each  group  is : 

BeO  =  25. 
A12O3=  1 02. 
SiO3  =  60. 


The  results  of  analysis  represent  the  proportion  in  which  the 
groups  are  present  in  the  molecule.  Consequently,  the  relation 
between  the  number  of  groups  must  be  : 

*  True  molecular  formulas  can  not  be  given  to  minerals,  for  they  are  volatile  or 
soluble  only  in  rare  instances,  and  are  probably  always  some  unknown  multiple  of 
the  empirical. 

231 


232  MINER  A  LOGY. 

Percentage  Atomic  Proportionate 

Composition.  Weights.  Number  of  Groups. 

14.01  ~  25  =  .56 

19.26  -f  102  =  .189 

66.37        -f         60         =  1.106 

Now,  as  fractional  atoms  cannot  exist,  our  problem  is  simply  to 
find  the  smallest  number  of  whole  groups  which  stand  to  each 
other  in  this  relation,  and,  as  .56  :  .189  :  1.106  =  3  :  I  :  6,  very 
nearly,  therefore,  the  composition  is  represented  by  3BeO  -f  A12O3 
-f-  6SiO2,  which  may  be  better  written  Be^A^SigO^,  or,  as  it  at  once 
becomes  evident  that  the  proportion  between  silicon  and  oxygen 
is  that  of  a  metasilicate,  Be3Al2(SiO3)6. 

It  will  now  be  found,  on  calculating  the  theoretical  percentage 
composition  of  Be3Al2(SiO3)6,  that  it  agrees  within  the  limits  of 
error  with  that  found  by  analysis,  and  as  the  twelve  affinities  of 
the  six  SiO3  radicals  are  satisfied  by  those  of  Be  and  Al  atoms,  the 
formula  probably  represents  the  composition  of  the  compound. 
The  true  molecular  formula  is,  however,  ?/Be3Al2(SiO3)6  wherein  n 
represents  some  whole  number.  In  this  way  the  formulas  of 
many  minerals  have  been  settled  beyond  question,  while  for  others 
this  success  has  not  been  reached. 

ISOMORPHISM.* 

Frequently  the  results  of  analyses  show  that  the  minerals  con- 
tain elements  foreign  to  their  true  composition.  These  may  be 
present  as  impurities  but  if  the  mineral  is  homogeneous  it  is 
usually  found  that  these  unexpected  elements  replace  analogous 
elements  of  the  true  molecule.  Many  beryls,  for  instance,  contain 
Cs,  H2,  Na2,  Ca,  or  Mg  replacing  Be;  and  Fe  or  Cr  replacing  Al. 
This  replacement  is  explained  by  the  principle  of  isomorphism. 

Isomorphous  Substances. 

Substances  are  said  to  be  isomorphous  if  they  fulfill  the  following 
conditions: 

(a)  Show  distinct  similarity  in  their  molecules  and  a  close  re- 
semblance in  their  reactions. 

*  Absolute  isomorphism  does  not  exist  except  in  the  isometric  substances.  The 
replacement  of  one  element  for  another  in  either  all  or  part  of  the  molecules  pro- 
duces some  change  in  the  angles. 


CHEMICAL    CHARACTERS    OF  MINERALS, 


233 


(b)  Crystallize  in  forms  which  in  the  regular  system  are  identical, 
and  in  the  other  systems  are  so  closely  related  as  to  require,  at 
times,  special  care  in  angle  measurement  to  recognize  any  differ- 
ence. 

(c)  Are  capable  of  mixing  in  varying  proportions  to  form  homo- 
geneous crystals. 

The  third  condition  is  the  most  important.*     The  others  have 
no  recognized  limit. 

For  instance  the  orthorhombic  sulphates  form  an  isomorphous  series. 


Species. 

Type 

Formula. 

Axial  Ratio. 
a:b:c. 

Prism  Angle, 
no:  iio. 

Dome  Angle, 

IO2  :  IO2. 

Barite 

BaSO4 

.815  :  i  :  1.313 

78°  22' 

77°  43' 

Celestite  
Anglesite  
Anhydrite  

SrSO4 
PbSO4 
CuS04 

.779  :  i  :  1.280 
.785:  i  :  1.289 
.893:  i  :i.oo8 

75°  50' 
76°  1  6' 
83°  33' 

78°  49' 
78°  47' 

These  not  only  occur  as  the  type  minerals  but  as  mixed  crystals  known  as  calcio- 
celestite,  barylocelestite,  leedsite,  etc. 

The  carbonates  form  two  characteristic  isomorphous  groups,  the  first  orthorhombic 
and  the  second  rhombohedral. 


Axial  Ratio, 
d     :  b  :      c. 

Aragonite,  CaCOs 622  :  i  :  .720 

Strontianite,  SrCOs 609  :  i  :  .724 

Witherite,  BaCOs 603  :  i  :  .730 

Cerussite,  PbCOs 610  :  i  :  .723 


Prism  Angle, 
119  A  iTo. 
63°  48' 
62°  41' 
62°   12' 
62°  46' 


Bromlite,   (Ba.Ca)CO3,  Emmonite,  (Sr.Ca)COs,  are  instances  of  mixed  crystals 
with  extensive  replacement.     Many  occurrences  show  smaller  replacement. 


Axial  Ratio  -  .  Rhombohedron. 

a 

Calcite,  CaCOs 854  74°  55' 

Siderite,  FeCO3 818  73°  o 

Smithsonite,  ZnCOs 806  72°  20' 

Magnesite,  MgCO3 811  72°  36' 

Rhodochrosite,  MnCOs 818  73°    o 

In  this  group  the  mixed  crystals  are  exceedingly  common  and  many  variety 
names  exist  usually  involving  the  name  of  the  principal  replacing  element  such  as 
manganocalcite,  ferriferous  rhodochrosite,  calciferous  siderite,  etc.  In  addition  there 
are  double  salts  such  as  dolomite,  CaMg(CO3)2,  and  subspecies  ankerite,  (CaCOs) 
(Mg.Fe.Mn)CO8. 

*  Retger's  rule  is:  "Two  substances  are  truly  isomorphous  if  the  physical  proper- 
ties of  their  mixed  crystals  are  continued  functions  of  their  chemical  composition." 


234 


MINERALOGY. 


Isomorphous  Mixtures  or  Homogeneous  Mixed  Crystals. 

When  two  or  more  isomorphous  substances  mix  to  form  homo- 
geneous crystals  the  resulting  solids  are  variously  called  "homo- 
geneous mixed  crystals,"  "isomorphous  mixtures"  and  "solid 
solutions."* 

Most  mineral  species  are  isomorphous  mixtures  and  their  color, 
specific  gravity,  fusibility  and  other  qualities  may  vary  widely 
in  consequence. 

Although  it  is  generally  held  that  mixed  crystals  consist  of 
isomorphic  molecules  united  "like  stones  in  a  building"  it  is 
convenient  to  regard  them  as  formed  by  the  replacement  of  one 
element  or  radical  by  another  isomorphous  with  it,  rather  than 
as  a  mixture  of  different  individual  molecules. 

The  principle  of  isomorphic  replacement  is  well  illustrated  in  the  garnets  which 
have  the  class  formula  R3//R2//'(SiO4)3  in  which  R"  stands  for  any  combination  of  the 
isomorphous  divalent  atoms  Ca,  Mg,  Fe",  Mn  taken  three  at  a  time  and  R'"  denotes 
any  combination  of  the  isomorphous  trivalent  atoms  Al,  Cr  or  Fe'". 

Therefore  while  the  typical  species 

Grossularite,    CasAMSiO^s  Spessartite, 

Pyrope,  Mg3Al2(SiO4)3  Andradite, 

Almandite,      FesA^CSiO-Os  Uvarovite, 

have  the  formulas  assigned  to  them;  when  pure  they  are  in  fact  seldom  found  on 
analysis  to  more  than  approach  these  formulas.     For  instance: 


Si02. 

A12O3. 

CaO. 

MnO. 

FeO. 

MgO 

Fe208. 

Grossularite: 

Vesuvius 

39.8 

20.16 

35.42 

0.46 

1.  21 

0.97 

1.03 

Jordansmiihl    .... 

37.8 

21.13 

31.28 

0.45 

4.19 

2.88 

Spessartite: 
Theoretical  

36.4 

20.60 

43.0 

Glen  Skiag  

35-99 

16.22 

O.4O 

15.24 

23.27 

0.47 

8.64 

Accordingly  garnets  vary  through  all  combinations  of  color,  with  wide  divergence 
of  composition.  Still  their  crystalline  forms  are  identical  and  their  composition 
can  be  expressed  as  of  a  definite  type. 

Formulas  of  Isomorphous  Mixtures. 

The  formulas  are  calculated  from  the  analyses  as  before  by 
dividing  the  percentage  composition  by  the  molecular  weight  of 
the  radical  (or  atomic  weight  of  the  element). 

*  The  term  solid  solution  includes  also  non-isomorphous  combinations.  Any 
solution  of  a  solid  in  a  solid. 


CHEMICAL    CHARACTERS    OF  MINERALS.  235 

For  instance,  the  spessartite  from  Glen  Skiag. 

Molecular  Number 

Percentage.  Weight.  Ratio.  of  Groups. 

MnO 15-24  -7-71  =  .2146"! 

FeO 23.27  -r        71.9  =  .3236  I 

MgO 0.47  -T-       40.36  =  .0116  f 

CaO 0.40  -5-       56.10  =  .oo7oJ 

AbOs.  .  .    16.22      -f-      102.2        =     .1587") 

}-     .2128  1.14 

Fe2O3 8.64      -f-      159.8        =     .0541 J 

SiO2 35-99      ^60  =      .5998         .5998  3-23 

This  only  approximates  a  garnet  formula,  giving 

3R"0,     i.i4R2'"03,     3.23Si02 

and  probably  indicates  some  loss  of  divalent  elements  by  weathering,  or  some  inter- 
mixed impurities. 

A  black  sphalerite  from  Felsobanya,  Hungary,  gave: 

Percentage.  Atomic  Weight.        Ratio.  Number  of  Groups. 

S 33-25 

Zn 50.02 

Fe 15.44 

>     1.040 
Cd 30 

Pb i. 01 

In  expressing  the  composition  of  an  isomorphous  mixture  by 
formulas  the  letter  R  is  used  to  represent  a  varying  group  of 
isomorphic  or  equivalent  elements,  and  it  may  have  the  valency 
of  these  elements  designated  by  dots  above  and  to  the  right  of 
the  letter.  When  elements  are  placed  in  a  parenthesis  with  a 
period  between,  as  (Zn.Fe)S,  it  means,  that  the  zinc  and  iron  taken 
together  are  equivalent  to  one  atom  of  sulphur. 

GEL   MINERALS   AND   ADSORPTION. 

There  are  a  series  of  mineral  products,  all  results  of  weathering 
or  hot  springs  action,  which  by  their  lack  of  uniform  composition, 
generally  amorphous  structure  and  external  appearance  suggest 
that  they  are  "hydrogels,"  that  is,  products  of  the  colloidal 
condition.  In  common  with  artificial  "hydrogels"  they  take  up 
or  "adsorb"  foreign  material  from  solution  in  proportions  inde- 
pendent of  molecular  weights  and  independent  of  crystalline 
similarity.  Although  such  "hydrogels"  are  homogeneous  and 
not  mechanical  mixtures,  they  are  like  solutions  rather  than 
definite  chemical  compounds  and  no  way  is  known  by  which  to 


236  MINERAL  OGY. 

tell  which  constituents  are  united  and  which  adsorbed.  No  con- 
stancy in  analysis  is  to  be  expected  and  no  good  formulas  will 
result. 

CHEMICAL   ALTERATIONS. 

The  results  of  alteration  through  atmospheric  agencies,  infiltra- 
tion of  water,  etc.,  tend  at  times  to  so  alter  the  individual  that  its 
composition  varies  widely  from  the  type.  New  species  may  form 
and  frequently  the  original  mineral  and  its  alteration  product 
may  both  be  present  in  the  same  fragment  or  crystal. 

In  general  the  new  material  is  softer  and  less  coherent  than  the 
original  and  the  microscope  quickly  proves  the  lack  of  homo- 
geneity. 

CHEMICAL   TYPES. 

Minerals  like  other  definite  chemical  compounds  are  either 
elements,  oxides,  acids,*  bases  or  salts,  the  last  being  by  far  the 
most  numerous. 

1.  The  Elements,  as  Au,  Ag,  Cu,  Sb,  C,  S.     These  are  frequently 
alloyed  with  other  elements  as  copper  with  silver,  sulphur  with 
selenium,    etc.     Only   about   one   fifth   of   the   known   elements 
occur  "native,"  that  is  as  minerals. 

2.  Oxides.     Elements   in   combination   with    oxygen,    such   as 
cuprite,  Cu2O,  cassiterite,  SnO2,  hematite,  Fe2O3.     Only  about  a 
dozen  are  sufficiently  common  to  be  described  in  this  book. 

3.  Hydroxides.     (Bases.)     Containing    hydroxyl    (OH)    as    an 
important  radical,   as  ^brucite,  Mg(OH)2,   limonite,    Fe4O3(OH)6. 
Very  few  of  these  are  described. 

4.  Acids.     The  only  example  described  is  sassolite,  H3BO3. 

5.  Salts.     Most  minerals  can  be  considered  as  derived  from 
known  or  hypothetical  inorganic  acids,  and  in  many  instances 
they  have  been  artificially  produced  in  the  laboratory  as  normal, 
acid  or  basicf  salts  of  these  acids. 

*  As  defined  under  the  ionic  theory: 

Acids  are  compounds,  the  dilute  water  solutions  of  which  contain  hydrogen  ions. 

Bases  or  hydroxides  are  compounds,  the  dilute  water  solutions  of  which  contain 
hydroxyl  "(OH)  ions. 

Salts  are  formed  by  union  of  base  with  acid,  water  also  forming. 

t  In  normal  salts  all  of  the  hydrogen  of  the  acid  or  hydroxyl  of  the  base  have  been 
replaced  by  metallic  elements  or  acid  radicals  respectively.  In  acid  salts  only  part 
of  the  hydrogen  has  been  replaced.  In  basic  salts  only  part  of  the  hydroxyl  has 
been  replaced. 


CHEMICAL    CHARACTERS    OF  MINERALS.  237 

The  most  important  groups  of  salts  are : 

The  Sulphides,  derivatives  of  H2S  and  to  a  less  extent  their 
analogues  the  selenides,  tellurides,  arsenides  and  antimonides,  as 
galenite,  PbS,  clausthalite,  PbSe,  hessite,  Ag2Te,  niccolite,  NiAs. 

The  Chlorides,  derivatives  of  HC1,  and  to  a  less  extent  their 
analogues  the  fluorides,  bromides  and  iodides  as  halite,  NaCl, 
fluorite,  CaF2,  bromyrite,  AgBr,  iodyrite,  Agl. 

The  Carbonates,  derivatives  of  H2CO3,  as  calcite,  CaCO3;  basic 
salts  of  carbonic  acid  also  occur,  as  malachite,  Cu2(OH)2CO3. 

The  Sulphates,  derivatives  of  H2SO4,  as  barite,  BaSO4. 

The  Phosphates,  derivatives  of  H3PO4,  as  vivianite,  Fe3(PO4)2 
+  8H2O. 

The  Silicates.  By  far  the  largest  subdivision.  They  may 
generally  be  considered  as  derivatives  of  orthosilicic  acid,  H4SiO4, 
as  chrysolite  (Mg.Fe)2SiO4,  metasilicic  acid,  H2SiO3,  as  rhodonite, 
MnSiO3,  or  some  hypothetical  polysilicic  acid,  as  H4Si3Og,  repre- 
sented by  orthoclase,  KAlSi3O8. 

Less  common  are:  nitrates,  derivatives  of  HNOs,  chromates,  derivatives  of 
HhCKX  and  of  HCrC>2,  molybdates,  derivatives  of  H2MoO4;  tungstates,  derivatives 
of  H2\VO4;  borates,  derivatives  of  HBO2,  HsBOs  or  of  H2B4O;  aluminates,  deriva- 
tives of  HA1O2;  arsenates,  derivatives  of  HsAsC^;  vanadinates,  derivatives  of  HsVCX; 
columbates,  derivatives  of  HCbOs;  sulpharsenites,  derivatives  of  HsAsSa  and  their 
analogues  the  sulphantimonides. 

Water  of  Crystallization. 

The  water  given  off  when  hydroxides  or  acid  or  basic  salts  are 
heated  is  usually  expelled  only  under  a  temperature  approaching 
a  red  heat.  Such  water  is  not  reassumed  in  the  presence  of  mois- 
ture, and  is  not  considered  to  be  present  in  the  mineral  as  water 
but  to  be  in  intimate  combination.  Its  loss  destroys  the  original 
mineral. 

In  other  minerals  water  is  given  off  at  relatively  low  tempera- 
tures, sometimes  at  common  temperatures  (laumontite) ,  some- 
times by  a  slight  increase  (gypsum)  or  below  300°,  natrolite. 
Such  water  is  frequently  reassumed  by  the  mineral  in  the  presence 
of  moisture  and  the  physical  properties  may  remain  unaltered. 
That  is  the  release  of  the  water  has  not  destroyed  the  original 
substance,  and  it  is  assumed  to  be  present  in  the  minerals  as  water 
(called  water  of  crystallization)  and  is  expressed  in  the  formula  as 
molecules  of  H2O,  thus  gypsum,  CaSO4  +  2H2O. 


238  MINERALOGY. 

MICROCHEMICAL    METHODS. 

"The  application  of  chemical  operations  to  the  examination 
and  study  of  very  small  quantities  of  material." 

The  tests  are  either  tests  for  elements  or  tests  which  by  color 
changes,  etchings,  etc.,  of  polished  surfaces  give  clues  to  species. 
Both  require  much  practice  and  are  as  yet  largely  reserved  for 
special  investigation  and  little  used  in  general  mineralogical 
testing.  The  recent  works  of  Chamot*  and  Murdoch!  should  be 
consulted. 

In  the  study  of  the  rock-forming  silicates,  especially  in  their 
more  minutely  crystallized  varieties,  tests  for  certain  great  ele- 
ments such  as  Al,  Ca,  Mg,  K,  Na  are  desirable  and  the  crystallized 
fluo-silicates  obtained  by  the  Boricky  method  by  treatment  of  the 
silicates  with  hydrofluoric  acid  as  well  as  the  series  of  crystals 
obtained  by  the  Behren's  method  by  treatment  with  hydrofluoric 
and  sulphuric  acids  and  subsequent  addition  of  different  reagents 
to  the  resulting  sulphate  solutions  are  used  to  some  extent.  Both 
are  described  in  Luquer's  "Minerals  in  Rock  Sections,"  pp.  136- 

139- 

A  few  microchemical  tests  and  re-crystallizations  are  described 
in  parts  of  the  book.  It  has  not  seemed  necessary  to  tabulate 
them. 

*  "Elementary  Chemical  Microscopy,"  John  Wiley  &  Sons,  1915. 

f  "Microscopical  Determination  of  Opaque  Minerals,"  John  Wiley  &  Sons,  1916. 


CHAPTER  XVII. 
THE   FORMATION   AND    OCCURRENCE    OF   MINERALS. 

The  solid  crust  of  the  earth  consists  almost  entirely  of  minerals, 
of  which  about  a  thousand  species  have  been  identified,  which 
involve  in  their  composition  practically  all  of  the  known  elements. 

But  the  vast  mass  of  the  crust  consists  of  aggregations*  of  a 
few  great  silicates  composed  almost  entirely  of  nine  elements 
themselves  calculatedf  to  constitute  over  98  per  cent,  of  the  crust 
in  the  following  proportions : 

0 49.85  Fe 4.12  Na 2.33 

Si 26.03  Ca 3.18  K 2.33 

Al 7.28  Mg 2. ii  H 0.97 

The  remaining  species  involving  the  eighty  elements  are  in  part 
disseminated  in  these  aggregations  or  rocksf  in  minute  amounts 
but  are  largely  concentrated  in  special  deposits,  pegmatite  veins, 
ore  veins,  contacts,  saline  residues,  etc. 

The  history  of  a  mineral,  the  r61e  it  has  played,  is  largely  told 
by  the  occurrence  and  associates  and  alternations  but  these  must 
be  considered  according  to  certain  fundamental  principles  of 
mineral  formation  which  have  been  revealed  by  consideration  of 
formations  still  going  on  and  laboratory  experiments. 

Associates  (Paragenesis). 

This  association  may  be  accidental,  as  in  a  conglomerate,  but 
the  association  in  the  rock  in  which  they  were  formed  may  reveal 
much  as   to   the  order  of   formation,  the  processes  which  were 
active,  and  the  temperature  and  pressure  during  formation. 
Alteration  and  Pseudomorphs. 

The  alterations  show  whether  the  changes  are  essentially  struc- 
tural, involving  a  molecular  rebuilding  or  essentially  chemical 

*  F.  W.  Clarke,  U.  S.  Geol.  Survey,  Bull.  491,  p.  33. 

fOf  the  remaining  1.8  per  cent,  ten  other  elements  in  order,  Ti,  Cl,  C,  P,  S,  Fl, 
Ba,  Mn,  Sr,  N,  are  estimated  to  total  1.33  per  cent,  leaving  0.47  for  the  remaining 
sixty-odd  elements. 

J  Aggregations  of  minerals  large  enough  to  be  of  geological  significance  and 
constant  enough  in  characters  to  be  identified  are  called  rocks. 

239 


240  MINERAL  OGY. 

with  oxidation,  reduction,  partial  solution,  or  the  entire  removal 
of  one  subvStance  and  its  replacement  by  another. 

Frequently  minerals  are  found  as  "pseudomorphs,"  that  is,  in 
crystalloids,  the  shapes  of  which  belong  to  some  other  mineral. 
In  many  instances  these  are  merely  casts  or  incrustations  which 
prove  little  as  to  the  process,  but  in  other  instances  they  are  evi- 
dently the  result  of  the  gradual  and  often  incomplete  alteration  of 
the  original  mineral  and  give  important  clues  to  the  process  of 
alteration  and  add  weight  to  synthetic  experiments  by  showing 
that  in  nature  similar  changes  actually  occur. 

Petrifactions  differ  from  pseudomorphs  principally  in  that  they 
are  alterations  or  replacement  of  organic  remains  by  mineral  sub- 
stances. 

Physical  and  Chemical  Characters. 

Any  conclusion  as  to  the  origin  or  mode  of  formation  of  a  min- 
eral must  be  in  conformity  with  its  observed  physical  and  chemical 
characters.  For  instance,  the  solubility  is  a  most  important  factor 
in  determining  the  order  of  separation  whether  from  aqueous  or 
fusion  solutions.  Leucite  crystals  are  isometric  in  shape,  but  their 
optical  characters  indicate  a  system  of  lower  symmetry  unless  the 
material  is  heated  to  433°  C,  the  conclusion  is  that  these  isometric 
crystals  formed  above  433°.  Cyanite  at  about  the  melting  point 
of  copper  assumes  the  characters  of  sillimanite,  hence,  ignoring 
the  effect  of  pressure,  it  formed  below  that  temperature. 

Synthetic  Production  of  Species  and  of  Alterations. 

The  successful  reproduction  of  a  mineral  by  a  method  which 
does  not  conflict  with  the  known  natural  conditions  is  an  important 
clue  as  to  its  probable  origin,*  but  is  not  conclusive,  for  the  same 
species  is  often  made  in  several  ways.  For  instance :  ortho- 
clase  has  been  formed  from  fused  magma,  from  sublimation  and  in 
the  wet  way  and  by  action  of  solutions  on  leu  cite,  and  galenite  has 

*  The  production  of  species  synthetically  has  several  other  purposes,  such  as  settling 
the  composition  : 

(a]  By  producing  crystals  identical  in  characters  with  those  of  some  natural  sub- 
stance but  avoiding  the  frequent  natural  inclusions,  weathering,  etc.,  which  lead  to 
varying  analyses. 

(£)   Obtaining  crystals  of  massive  or  poorly  crystallized  minerals. 

(c)  Obtaining  simple  types  which  are  rare  in  nature  and  rinding  new  members  of 
series. 


FORMATION  AND    OCCURRENCE    OF  MINERALS.      241 

been  formed  by  sublimation,  by  electrochemical  reactions  and  by 
superheated  water  in  a  sealed  tube. 

On  the  other  hand,  probable  theories  which  have  not  been  synthe- 
tically checked  are  not  necessarily  wrong.  The  processes  of  nature 
are  not  all  to  be  reproduced,  especially  the  geologic  periods  of  time. 

So  also  the  alteration  of  a  mineral  in  the  laboratory  or  even  the 
production  of  pseudomorphs  by  possible  natural  methods  may 
be  of  value  as  indicating  what  would  happen  under  similar  condi- 
tions maintained  longer  periods. 

The  method  of  synthesis  chosen  must  conform  as  far  as  possible 
with  the  observed  conditions,  must  employ  reagents  that  occur  in 
nature  and  are  thought  to  have  taken  part  in  the  making.  Geo- 
logic time  may  be  in  part  compensated  for  by  increased  pressure 
and  a  temperature  of  1 00°  to  300°;  microscopic  crystalline  crusts 
must  often  be  accepted  as  the  equivalent  of  larger  natural  crystals. 

THE   PROCESSES    OF   MINERAL   FORMATION. 

The  processes  of  mineral  formation  may  be  broadly  grouped 
under  the  headings: 

1.  Crystallization  from  molten  silicate  magmas. 

2.  Formation   by  pneumatolysis,  that   is,   processes   in   which 
gases  and  vapors  play  a  prominent  part. 

3.  Crystallization  or  precipitation  from  aqueous  solutions. 

CRYSTALLIZATION   FROM    MOLTEN    SILICATE    MAGMAS. 

Below  the  present  crust  of  the  earth  the  regularly  increasing 
temperature  and  pressure  indicate  that  at  some  depth  everything 
must  be  a  fluid  mass.  This  fluid  mass  or  magma  by  volcanic 
forces  penetrates  any  crack  or  crevice  in  the  crust  above,  some- 
times reaching  and  overflowing  at  the  surface  (volcanic  rocks)  at 
other  times  being  forced  between  strata  far  below  the  surface 
(plutonic  rocks). 

The  Nature  of  a  Magma. 

The  fluid  magma  consists  chiefly  of  silicates  but  partly  of 
oxides,  sulphides,  fluorides  and  ferrates  mutually  dissolved  in  each 
other  with  certain  volatile  constituents,  chiefly  water. 

As  it  cools  the  various  minerals  separate  partly  as  type  species, 
partly  as  mixed  crystals. 
17 


242  MINERAL  OG  Y. 

The  order  of  separation  rests  more  on  solubility  than  fusibility* 
and  much  upon  eutectic  ratios,  for  in  a  cooling  mass  if  more  than 
the  proportion  of  one  constituent  is  present  than  is  necessary  to 
form  the  "eutecticum"  or  mixture  with  lowest  melting  point 
that  constituent  would  separate  first.t 

Other  factors  such  as  supersaturation  exist,  the  number  of 
components  is  considerable,  the  composition  of  the  magma  is 
constantly  changing  and  the  problem  is  very  complex. 

FORMATION   BY   PNEUMATOLYSIS. 

Pneumatolysis  is  Bunsen's  name  for  those  processes  in  which 
gases  and  vapors  play  an  important  part.  Aqueous  solutions 
may  contribute  to  the  reaction. % 

Usually,  the  term  is  limited  to  the  action  of  gases  and  vapors  on 
preexisting  minerals,  but  is  here  allowed  to  include  certain  minor 
processes. 

The  Gases  and  Vapors. 

Volcanoes  emit  much  steam§  and  relatively  small  amounts  of 
other  vapors,  often  at  first  O  and  N,  mixed  about  as  in  air,  and  a 
little  H,  and  later,  probably  by  the  action  of  the  steam  and  the 
high  temperature  in  decomposing  existing  compounds,  there  arise 
vapors  of  HC1,  SO3,  SO2,  H2S,  CO2,  CO,  Cl,  CH4,  HF,  SiF2,  B2O3. 

Similar  gases  and  vapors  are  released  from  slowly  cooling  magma 
which  force  themselves  into  the  already  solidified  magma  and  the 
neighboring  rocks  and  produce  new  minerals  and  recrystallizations. 

The  gases  and  vapors  act  as  solvents  and  also  as  "mineralizers" 
much  as  in  the  many  experiments  with  sealed  tubes  and  frequently 
the  action  is  catalytic  as  in  many  such  experiments. 

Pneumatolytic  action  has  occurred : 

*  Quartz  fusible  at  1625°  often  begins  to  crystallize  at  noo  to  1200°.  Vesuvius 
lavas  are  still  molten  at  1100°.  The  nearly  infusible  leucite,  for  instance,  in  a 
leucite-tephrite  magma  goes  into  a  solution  at  a  little  above  red  heat  and  separates 
at  a  red  heat. 

t  For  instance,  the  eutecticum  of  chrysolite  MgzSiO4  and  diopside  CaMaSi2O6 
is  32  per  cent,  chrysolite,  68  per  cent,  diopside.  In  a  cooling  mass  if  more  than  32 
per  cent,  chrysolite  were  present  chrysolite  would  separate  first,  with  less  chrysolite 
diopside  would  separate  first. 

J  Above  the  critical  temperature,  which  for  water  is  375°  C.,  physical  differ- 
ences between  the  gaseous  and  liquid  conditions  cease. 

§  One  minor  cone  of  Etna  is  estimated  to  have  discharged  vapor  at  rate  of  4,620,000 
gallons  per  day. 


FORMATION  AND    OCCURRENCE    OF  MINERALS.     243 

(a)  Around  volcanoes  by  action  of  vapors  and  gases  on  country 
rock  and  on  minerals  already  formed  from  exhalations. 

(b)  In  pegmatite  veins. 

(c)  In  contacts. 

(d)  In  and  near  tin  lodes. 

(e)  In  some  apatite  veins. 

(/)  In  silver  and  gold  veins  near  younger*  eruptives. 

Minor  Processes  Involving  Gases  and  Vapors. 

In  certain  instances  the  formation  does  not  involve  preexisting 
solids  but  is  either 

(a)  Due  to  the  mixing  of  two  gases  or  vapors. 

(b)  Due  to  the  decomposition  of  gases  or  vapors  by  heat. 

In  other  instances  "sublimates"  form  at  cooling  which  may 
be  true  sublimates,  involving  no  change  of  chemical  composi- 
tion or  may  be  of  more  complicated  origin. 

CRYSTALLIZATION    OR    PRECIPITATION  FROM    WATERY    SOLUTIONS. 

Water  is  the  chief  agent  in  the  alteration  and  concentration  of 
minerals. 

Distilled  water  at  ordinary  temperatures  and  pressures  will  dissolve  large  amounts 
of  the  soluble  salts  and  small  amounts  of  almost  all  other  substances,  for  instance,  in 
per  cents,  gypsum  0.25,  calcite  0.0025,  barite  0.0002;  anhydrous  silicates  very  slightly 
and  quartz  so  slightly  that  no  numbers  have  yet  been  found  to  express  it.  Increased 
temperature  and  pressure  in  general  increase  solubility. 

Rain  Water. 

Rain  water  is  the  principal  cause  of  the  decay  or  weathering  of 
rocks.  In  passing  through  the  atmosphere  it  absorbs  about  0.65. 
per  cent,  oxygen  and  0.03  per  cent,  carbon  dioxide.  This  charged 
water  possesses  greatly  increased  solvent  power  and  an  oxidizing 
action. 

For  instance,  water  saturated  with  COz  dissolved  o.io  to  0.12  per  cent,  of  calcite 
or  forty  times  as  much  as  pure  water. 

More  important,  however,  as  bearing  upon  the  alteration  of  silicates,  is  that 
water  containing  carbonic  acid  or  alkaline  carbonates  in  solution  will  decompose: 
many  silicates. 

Free  oxygen  may  oxidize  sulphides  and  arsenides  and  further  oxidize  oxides  or 
even  drive  out  COz,  for  instance  forming  hematite  from  siderite,  4FeCOs  +  2O  + 
3H20  =  2Fe2O3 


*  Called  propylization  and  consisting  in  the  change  of  the  original  minerals  of 
the  eruptive  to  chlorite,  clay,  calcite,  pyrite,  etc. 


244  MINERAL  OG  Y. 

Rain  water  also  mechanically  sorts  and  transports  the  less 
soluble  portions  and  by  streams  carries  the  soluble  portions  to 
marshes,  lakes  and  seas,  where  ultimately  by  evaporation  new 
mineral  deposits  develop. 

The  minerals  are  not  attacked  with  the  same  rapidity,  the 
presence  of  certain  elements  seeming  to  be  the  principal  determin- 
ing factor: 

Calcium  bearing  minerals  are  most  readily  attacked  and  the  CaO  is  largely 
carried  away. 

The  alkalis,  soda  and  potash,  also  form  soluble  salts  but  the  Na2O  is  principally 
carried  off  in  solution,  while  the  K2O,  to  a  great  extent,  recombines  to  new  species. 

Magnesium  is  slightly  carried  off  but  for  the  most  part  forms  hydrous  magnesia 
minerals. 

Ferric  oxide  is  not  much  attacked.  Ferrous  oxide  largely  combines  with  oxygen 
and  water  to  form  limonite. 

Most  of  the  alumina  and  silica  remain  but  with  some  formation  of  colloidal 
aluminous  silicates  and  silicic  acid. 

The  leached  products  possess  a  certain  power  to  reabsorb  lost  substances,  clays 
and  soils  take  up  potash,  hydroxides  of  iron  also  absorb. 

Underground  Water. 

The  rain  water  in  part  sinks  through  the  soil,  penetrating  by 
pores  and  fissures  to  considerable  depths,*  and  with  infiltra- 
tions from  lakes,  ocean  and  water  courses  and  smaller  amounts  of 
water  from  ancient  sediments  or  released  by  cooling  magmas, f 
forms  the  so-called  "underground  or  ground  water." 

In  the  upper  portions  there  is  free  circulation,  the  action  is 
essentially  that  of  rain  water,  solution  and  oxidation  and  much 
of  the  water  returns  to  the  surface  by  springs. 

Lower  there  is  less  circulation,  the  water  is  poorer  in  oxygen  than 
rain  water,  but  contains  in  solution  such  salts  as  carbonates  of 
calcium,  magnesium,  potassium  and  sodium,  or  locally  chlorides 
and  sulphates. 

The  action  is  more  varied  than  at  or  near  the  surface. 

Organic  materials  may  cause  reduction  to  lower  oxides  or  native 
metals,  and  of  alkaline  sulphates  to  sulphides,  which  then  are  able 
to.  precipitate  sulphides  from  silicates,  carbonates  and  sulphates 
of  the  metals.  Under  the  increased  pressure  the  water  tends  to 
enter  into  combination. 

*Said  in  extreme  cases  to  be  10,000  feet. 

t  Cooling  igneous  rocks  and  late  phases  of  an  intrusion  may  release  water  often 
carrying  in  solution  metallic  ores,  sulphur,  boron,  fluorine,  etc. 


FORMATION  AND    OCCURRENCE    OF  MINERALS.     245 

THE  SEPARATION  OF  SOLID  COMPOUNDS  FROM  WATERY  SOLUTIONS. 

The  principal  methods  by  which  the  constituents  of  a  watery 
solution  are  separated  from  the  solution  as  solids  are : 

I.  Decreased  Solvent  Power  by : 

(a)  Decreased  pressure  or  temperature,  as  in  the  case  of  solutions 
rising  from  below. 

(b)  Evaporation.  —  This  is  practically  restricted  to  the  seas  and 
lakes  at  the  surface,  as  in  the  interior  the  hollows  are  soon  filled 
with  water  vapor. 

(c)  Loss  of  a  Constituent.  —  A  loss  of  CO2  takes  place  in  mov- 
ing water  in  contact  with  air,  as  at  outlets  of  springs  or  rivers. 

(d)  Solution  of  Another  Substance.  —  Solutions  saturated  with 
one  substance  can  dissolve  another,  but  a  saturated  complex  solu- 
tion contains  less  of  either  salt  than  when  saturated  by  it  alone. 
Hence  a  saturated  solution  coming  in  contact  with  a  new  sub- 
stance may  dissolve  some  of  it,  but  if  so  will  deposit  some  of  the 

'substance  previously  in  solution. 

II.  Precipitation. 

The  precipitation  of  a  mineral  may  take  place  as  follows: 

(a)  As  the  result  of  the  meeting  of  two  solutions. 

(b)  By  the  action  of  gases  upon  a  solution. 

(c)  By  electrolytic  action,  probably. 

(d)  By  the  action  of  a  solid  upon  a  solution. 

Very  dilute  solutions  and  slow  action  are  favorable  to  well- 
developed  crystalline  material. 

The  law  of  mass  action  rules,  that  is,  each  material  exerts  chemical  action  pro- 
portionate to  its  mass.  Exactly  opposite  results  are  obtainable;  for  instance, 
BaCOs  with  sufficient  sulphate  solution  is  all  changed  to  BaSC>4  and  BaSO4  with 
sufficient  carbonate  solution  is  all  changed  to  BaCOs.  If  the  quantity  of  solution  is 
not  sufficient,  a  stage  is  reached  in  which  both  salts  are  simultaneously  in  solution. 

III.  Metasomatic  Replacement. 

Replacement,  or  metasomatic  replacement,  while  often  involving 
a  complicated  series  of  chemical  reactions,  implies  always  the 
action  of  a  solution  on  an  existing  mineral  in  such  a  way  that  as 
each  particle  of  the  mineral  is  dissolved  it  is  immediately  replaced 
by  a  particle  of  another  mineral  of  different  chemical  composition. 

MINERAL   OCCURRENCES. 

The  occurrence  of  minerals  may  be  discussed  under  the  following 
headings: 


246  MINERAL  OG  Y. 

A.  The  Great  Mineral  Aggregates  or  Rocks. 

B.  The  Minerals  Produced  During  the  Cooling  of  a  Magma. 

1.  The  Minerals  which  Crystallize  from  Molten  Silicate 

Magmas. 

2.  Pegmatite  Veins  and  their  Minerals. 

3.  Magma  tic  Segregations  and  their  Minerals. 

4.  Zeolites. 

5.  The  Minerals  Formed  near  Volcanoes. 

C.  The  Minerals  Produced  by  Weathering  and  the  Weathering 

Solutions. 

6.  The  Minerals  of  the  Mechanical  Sediments. 

7.  The  Minerals  of  the  Chemical  Sediments. 

8.  The  Minerals  of  the  Sediments  due  to  Organisms. 

D.  Metamorphic  Minerals  and  Vein  Minerals. 

9.  The  Minerals  of  Contacts. 

10.  The  Minerals  of  Regional  Metamorphism. 

11.  The  Minerals  of  Veins  and  Replacements. 

A.     THE   GREAT   MINERAL   AGGREGATES   OR   ROCKS. 

Practically  all  minerals  are  constituents  of  igneous,  sedimentary, 
or  metamorphic  rocks. 

Igneous  or  Eruptive  Rocks. 

About  ninety-five  per  cent,  of  the  crust  of  the  earth  consists 
of  rocks  which  come  from  the  interior  of  the  earth  as  molten 
silicate  magmas.  See  page  241.  These  molten  magmas  were 
forced  up  into  crevices  in  the  crust  above,  sometimes  reaching 
and  overflowing  at  the  surface  (volcanic  rocks*),  at  other  times 
formed  deep  within  the  earth  (plu tonic  rocksf). 

Evidently  the  same  magma  may  form  both  plutonic  and  volcanic 
rocks  containing  essentially  the  same  mineral  species. 

The  great  plutonic  and  volcanic  rocks  and  their  dominant  minerals  are: 

*  The  volcanic  rocks  having  cooled  rapidly  are  often  glassy,  or  fine-grained  with 
constituent  minerals  unrecognizable  to  the  eye  alone  or  with  flow  structures  and 
steam  cavities.  Below  the  surface  they  show  less  glass  and  more  and  larger  crystals 
often  with  glassy  inclusions. 

f  The  plutonic  rocks  having  cooled  slowly  at  great  depths  are  solid  and  coarsely 
crystalline  with  recognizable  constituent  minerals  and  do  not  often  contain  glassy 
inclusions.  Liquid  inclusions  are  frequent. 


FORMATION  AND    OCCURRENCE    OF  MINERALS.     247 

Plutonic.  Volcanic.  Dominant  Minerals. 

Granite Rhyolite Quartz  and  orthoclase. 

Syenite Trachyte Orthoclase  with  mica  or  hornblende. 

Diorite Andesite Plagioclase  with  hornblende  or  biotite. 

Gabbro Basalt Plagioclase  with  pyroxene  or  chrysolite. 

Peridotite Chrysolite  pyroxene,  hornblende. 

The  Sedimentary  Rocks. 

The  volcanic  rocks  and  the  plutonic  rocks  which  by  erosion  or 
upheaval  reach  the  surface  undergo  a  process  of  breaking  down 
partly  chemical,  partly  mechanical,  by  the  combined  action  of 
rainwater  with  its  contained  oxygen  and  carbonic  acid,  unequal 
expansion  due  to  varying  temperatures,  the  action  of  glaciers, 
living  and  decaying  organic  matter  and  other  factors. 

The  residual  solid  material  and  the  weathering  solutions  form 
new  so-called  sedimentary  rocks,  which  in  general  are  stratified 
and  less  firm  and  coherent  than  igneous  rocks. 

The  Mechanical  Sediments. 

The  residual  solid  material  is  to  some  degree  mechanically 
sorted  by  water,  wind  or  glaciers  into  the  coarser  grains  containing 
more  unaltered  material  and  finer  grains  containing  more  colloidal 
and  hydrated  material.  By  pressure  and  the  cementing  action 
of  materials  deposited  from  percolating  waters  these  deposits 
of  gravel,  sand  and  clay  are  reconsolidated  into  conglom- 
erates, sandstones  and  shales,*  the  shales  being  by  far  the  most 
abundant. 

*  Average  compositions  are : 

Sandstones  (Clarke).     Shales  (Leith  and  Meade). 

Quartz 66.8  3I-9I 

Feldspars 11.5  17.60 

Clay 6.6  10.00 

Iron  hydroxides 1.8  4.75 

Carbonates n.i  7.90 

Sericite 18.40 

Other  minerals 2.2  9-44 

The  sandstones  and  conglomerates  consist  for  the  most  part  of  visible  fragments 
of  the  minerals  of  the  igneous  rocks,  cemented  by  calcium  carbonate,  silica,  clay, 
ferric  hydroxide,  calcium  and  barium  sulphates. 

The  shales  form  from  finer  particles  with  much  colloidal  material  (silicic  acid, 
clay,  etc.)  and  adsorbed  alkalis  and  alkaline  earths.     In  drying  the  colloidal  material  • 
almost  disappears,  fine-grained  quartz  and  white  mica  (sericite)  develop  and  much 
of  th*e  hydrous  iron  oxide  is  reduced  and  combined  to  chlorite,  siderite  or  pyrite. 


248  MINERALOGY. 

The  Chemical  Sediment. 

The  solutions  consequent  upon  the  breaking  down  or  weathering 
of  rocks  are  in  part  redeposited  in  the  mechanical  sediments  as 
cements  in  part  precipitated  in  other  rocks,  but  much  of  it  is 
carried  away  to  rivers,  lakes  or  oceans,  and  there  may  form 
deposits. 

If  these  form  without  the  assistance  of  organisms,  vegetable  or 
animal,  they  are  known  as  chemical  sediments.* 

The  "rocks"  which  are  chemical  sediments  are  chiefly  anhydrite,  gypsum  and 
halite  or  rock  salt;  locally  there  are  other  deposits  such  as  the  potassium  deposits 
of  Stassfurt,  the  soda  nitre  of  Chili  and  various  borates  which  have  geological  sig- 
nificance. 

Sediments  Due  to  Organisms. 

These  include: 

1.  The  inorganic  portion  of  skeletons  of  animals  and  plants 
consist  mostly  of  carbonate  of  lime,  some  of  phosphate  of  lime, 
some  of  silica. 

2.  The  organic  substance  usually  of  plants,  partly  of  animals, 
such  as  coal  or  petroleum. 

3.  Living  and  dead  organisms  may  act  to  precipitate  sediments, 
as  when  plants  expel  CO2  and  become  coated  with  CaCO3  or 
albumen  generates  ammonium  carbonate,  precipitating  CaCO3. 

The  "rocks"  belonging  to  this  division  are  the  limestones  and  dolomites,  the 
phosphate  rock,  coal  and  some  silica  deposits  such  as  diatomaceous  earth. 

Metamorphic*  Rocks. 

Both  igneous  and  sedimentary  rocks  are  greatly  altered  by 
the  intense  horizontal  pressures  which  cause  rock  folding  or 
mountain  making.  Not  only  is  a  lamellar  structure  developed 
but  under  the  pressure  and  resultant  heat  the  circulating  waters 
effect  recrystallizations  and  molecular  rearrangements  "in  place" 
usually  with  decrease  of  volume,  that  is,  denser  minerals.  Often 
water  is  introduced  as  in  amphibole,  chlorite  and  mica. 

The  resultant  rocks  are  essentially  alike  whether  formed  from 
igneous  or  sedimentary  rocks. 

Quartzites  form  from  sandstone  and  from  silica  precipitated  by  organisms.  Slates 
form  from  shales.  Mica  schists  form  from  shales,  sandstones  and  igneous  rocks. 

*  While  strictly  any  change  in  composition  or  structure  is  metamorphism  the  term 
is  generally  reserved  for  strongly  marked  changes  such  as  clay  shale  to  mica  schist. 


FORMATION  AND    OCCURRENCE    OF  MINERALS.     249 

Hornblende  schists  or  amphibolites  form  from  basic  igneous  rocks  rich  in  pyroxene; 
chlorite  schists  form  from  rocks  rich  in  iron  and  alumina  silicates.  Gneisses  form 
from  different  igneous  and  sedimentary  rocks. 

B.     THE   MINERALS  FORMED    DURING  THE   COOLING   OF  A   MAGMA. 

1.  The  Minerals  which  Separate  from  the  Liquid  Magma. 

The  average  composition*  of  igneous  rocks  is  not  greatly  dif- 
ferent from  that  already  given  p.  239  for  the  average  composition 
of  the  crust  of  the  earth. 

In  any  given  magma  many  possible  combinations  exist,  and 
the  same  magma,  solidifying  under  different  conditions,  may  yield 
different  minerals. 

In  general  all  the  K,  Na  and  Ca  and  most  of  the  Mg,  Al  and  Fe  unite  with  oxygen 
and  silicon  to  form  silicates.  Excess  of  Si  separates  as  SiOz  and  relatively  small 
amounts  of  Fe  and  Al  form  oxides,  ferrates  and  aluminates  and  Mg  may  combine  as 
an  aluminate. 

Experience  shows  that  the  number  of  minerals  which  actually  form  is  greater  in 
the  medium  basic  magmas  than  in  the  highly  siliceous  or  very  basic  magmas. 

Taking  an  average  of  some  700  described  igneous  rocks,  Clarke 
estimates  that  a  few  great  groups  constitute  an  overwhelming 
proportion,  although  in  particular  instances  other  groups  may 
dominate.  He  gives  as  the  proportions: 

1.  The  feldspars 59.5  per  cent. 

2.  The  pyroxenes  and  amphiboles 16.8    ' 

3.  Quartz 12.0    " 

4.  The  micas 3.8    "       " 

5.  Accessory  minerals 7.9    "       " 

100.0    "       " 

In  addition  to  the  great  groups  mentioned  other  important 
primary  minerals  in  certain  igneous  rocks  are: 

The  Feldspathoids,  nephelite,  leucite,  sodalite,  haiiynite,  noselite. 

The  Chrysolite  Group.     Chrysolite,  fayalite,  etc. 

Tourmaline  and  topaz  in  regions  near  pneumatolytic  action. 

Garnet  in  its  varieties  pyrope,  andradite,  almandite  and  spessar- 
tite. 

Corundum  and  spinel  in  rocks  rich  in  alumina. 

*  On  basis  of  1,000  to  1,500  analyses  O  47.05,  Si  28.26,  Al  7.98,  Fe  4.47,  Ca  3.43, 
Mg  2.34,  Na  2.54,  K  2.50.  Of  the  remaining  1.43  per  cent.  Ti  0.45,  H  0.16,  C  0.13, 
P  o.ii,  S  o.n,  Ba  .097.  Clarke,  Bulletin  491,  U.  S.  Geol.  Survey,  p.  27. 

t  Ibid.,  p.  31. 


250  MINERAL  OGY. 

The  Accessory  or  Minor  Primary  Minerals. — Certain   minerals  are  sometimes 
present  in  igneous  rocks  in  small  amounts  among  which  are: 
Elements,  graphite,  diamond,  iron,  copper,  gold,  platinum. 
Sulphides,  pyrrhotite,  pyrite,  pentlandite,  molybdenite,  millerite. 
Oxides*    magnetite,  hematite,  ilmenite,  chromite,  rutile,  brookite,  hausmannite, 

cassiterite. 

Silicates,  allanite,  analcite,  iolite,  sillimanite,  titanite,  zircon. 
Sundries,  apatite,  calcite,  fluorite,  monazite. 

2.  Pegmatite  Veins  and  their  Minerals. 

Igneous  rocks  are  often  cut  by  dikes  or  veins  consisting  chiefly 
of  coarse  and  even  gigantic  crystals  of  the  common  minerals  of 
the  igneous  rock,  and  usually  a  large  number  of  other  minerals 
which  are  in  part  the  accessory  minerals  of  the  igneous  rock,  in 
part  minerals  containing  the  same  elements  combined  with  water, 
fluorine,  chlorine,  boron  and  in  part  combinations  of  elements 
not  observed  in  the  igneous  rock.  Crystal  druses  are  frequent. 

These  veins  are  believed  to  represent  a  late  stage  of  solidification 
in  which  the  magma,  thinned  both  by  the  loss  of  the  already 
solidified  minerals  and  by  the  release  of  the  volatile  substances 
dissolved  therein  under  pressure,  penetrates  cracks  both  in  the 
solidified  portion  and  in  the  surrounding  rock. 

The  Minerals  of  Pegmatites. 

While  there  are  pegmatites  of  most  of  the  plutonic  rocks  the 
granitic  pegmatites  and  the  elaeolite-syenite  pegmatites  are  most 
important  and  contain  the  greatest  variety  in  minerals. 

In  granitic  pegmatites  the  typical  species  which  often  develop 
as  large  or  giant  crystals  are  feldspars  (chiefly  orthoclase  and 
microcline,  often  intergrown  with  albite),  quartz,  mica  (chiefly 
muscovite  or  lepidolite,  less  biotite) ,  tourmaline  (dark  in  compact 
rock  often  colored  in  the  druses),  spodumene,  and  beryl. 

Very  widely  distributed  species  are  apatite,  zircon,  titanite, 
fluorite,  topaz,  rutile,  monazite,  columbite. 

Where  the  vein  penetrates  other  rock  it  may  take  up  con- 
stituents therefrom  and  develop  such  minerals  as  garnet,  andalu- 

*  Ferrates,  chromates,  etc.,  included. 

t  In  certain  localities  Weinschenck  describes  pegmatites  due  to  rock  pressure, 
these  lack  the  crystal  druses  and  may  be  dense  mica-like  masses  with  enclosed  large 
crystals  such  as  the  Lisens  andalusite  and  the  enormous  25  m.  long  quartz  of  Zillerthal. 


FORMATION  AND    OCCURRENCE    OF  MINERALS.     251 

site,   zoisite,    phlogopite,    sillimanite,    cyanite,    staurolite,    iolite, 
spinel,  corundum,  possibly  diamond. 

Minor  minerals  in  granite  pegmatites  are  allanite,  amblygonite,  brookite, 
cassiterite,  chrysoberyl,  euclase,  fergusonite,  gadolinite,  graphite,  ilmenite,  magnetite, 
molybdenite,  petalite,  phenacite,  samarskite,  triphyllite,  uraninite. 

In  Nepheline-Syenitic  Pegmatites  the  great  minerals  are  the 
soda  feldspars,  albite  and  anorthoclase,  the  soda  pyroxenes,  acmite 
and  segirite,  the  soda  amphiboles  barkivikite  and  arfvedsonite, 
nephelite,  sodalite,  concrinite,  zircon. 

In  addition  there  are  a  host  of  rare  silicates,  titanites,  zirconates,  columbates, 
tantalates  and  other  compounds  of  both  common  and  rare  elements. 

A  few  of  these  species  are  astrophyllite,  eudialyte,  euxenite,  lavenite,  mosandrite, 
polycrase,  pyrochlore,  rinkite,  thorite,  wohlerite. 

In  still  other  varieties  of  pegmatites  there  may  be  developed 
large  crystals  of  apatite,  wernerite,  labradorite,  hypersthene,  green 
hornblende,  pyroxene,  rutile. 

The  economically  important  minerals  of  the  pegmatites  are  numerous  and  include 
not  only  quartz,  feldspar  and  mica  but  cassiterite,  wolframite,  the  minerals  of 
yttrium  and  thorium,  zircon,  apatite,  and  the  lithium  minerals. 

3.  Magmatic  Segregations  and  their  Minerals. 
The  eruptive  rocks  of  a  district  may  have  such  chemical  char- 
acters in  common  and  such  gradations  into  one  another  as  to 
indicate  that  they  are  due  to  splitting  up  or  "differentiation" 
of  one  homogeneous  rock  magma  into  several  by  the  segregation 
of  certain  constituents.  It  is  believed  that  the  changes  take  place 
chiefly  before  the  magma  is  forced  up.* 

The  Minerals  of  Magmatic  Segregations. 

The  minerals  which  segregate  are  the  minerals  which  first 
crystallize,  that  is: 

Oxides,  magnetite,  ilmenite,  chromite,  corundum,  rutile,  cas- 
siterite. 

Sulphides,  pyrrhotite,  pentlandite,  chalcopyrite,  pyrite,  molyb- 
denite. 

Elements,  iron,  platinum,  copper,  gold. 

The  rocks  involved  are  chiefly  basic  gabbro,  peridotite,  norite, 
occasionally  acidic  granite. 

*  The  high  specific  gravity  5.6  of  the  earth  as  a  whole  in  comparison  to  2.7  to  2.8 
for  its  crust  suggests  an  interior  segregation  of  the  heavier  materials  near  the  center. 


252  MINERALOGY. 

4.  Zeolites. 

The  formation  of  zeolites,  in  the  cavities  in  basic  lavas,  peg- 
matite dikes  and  ore  veins  is  probably  the  last  phase  of  con- 
solidation of  a  magma.  Their  rarity  in  veins  suggests  the  need  of 
stagnant  waters.  The  process  is  not  well  understood  and  is 
intimately  connected  with  the  method  of  formation  of  metallic 
copper. 

The  best  known  zeolites  are:  heulandite,  stilbite,  laumontite,  chabazite,  analcite, 
natrolite,  thomsonite. 

5.  The  Minerals  formed  near  Volcanoes. 

These  rising  vapors  act  on  the  sides  of  the  crevices  and  react 
upon  each  other,  producing  many  minerals  in  small  amounts,  the 
principal  groups  being: 

Sulphur  by  the  reaction  SO2  +  2H2S  =  38  +  2H2O. 

Oxides*  by  the  decomposition  of  chlorides  at  high  temperature. 

Carbonates  by  the  action  of  CO2  on  the  oxides. 

If  the  flowing  lava  passes  over  vegetable  matter  sal-ammoniac 
(NH4C1)  is  formed. 

Chlorides  and  sulphates  may  form  by  action  of  the  vapors  on 
the  adjacent  rocks.  A.  Scacchi  gives  a  large  list  but  those  in 
quantity  at  Vesuvius  are  chiefly  al unite  and  gypsum. 

Other  minerals  are,  amphibole,  tourmaline,  topaz,  phlogopite,  chondrodite, 
vesuvianite,  epidote,  fluorite. 

The  hot  solutions  near  extinct  volcanoes  often  produce  at  and 
near  the  surface  potash  minerals,  sericite,  adularia,  alunite  and 
other  species  such  as  gypsum,  jarosite,  fluorite,  barite,  calcite, 
chlorite,  epidote. 

C.     THE    MINERALS    PRODUCED    BY    WEATHERING    AND    THE 
WEATHERING   SOLUTIONS. 

These  may  be  considered  as  constituting  the  following  "Occur- 
rences''^ 

.6.  The  Mechanical  Sediments. 
7.  The  Chemical  Sediments. 

*  A  crack  in  lava  at  Vesuvius  in  1817  was  filled  in  10  days  with  a  3-ft.  thick  deposit 
of  hematite. 

t  The  gossans  or  oxidized  portions  of  ore  deposits  are  due  to  the  weathering  solu- 
tions but  are  considered  later. 


FORMATION  AND    OCCURRENCE    OF  MINERALS.     253 

8.  The  Sediments  of  Organic  Origin. 

As  previously  stated,  p.  244,  part  of  the  weathering  solutions 
penetrate  and  join  the  underground  water. 

6.  The  Minerals  of  the  Mechanical  Sediments. 

The  minerals  will  be  either 

(a)  Minerals  in  fragments  of  the  original  rock. 

(&)   New  minerals. 

The  minerals  from  the  original  rock  need  not  be  listed  except  to 
say  that  a  few  species  dominate  such  as  quartz,  feldspars  and 
micas.  The  accessory  minerals,  magnetite,  zircon,  corundum, 
ilmenite,  chromite,  tend  to  accumulate. 

The  New  Minerals. 

Comparatively  few  form,  the  principal  ones  being 

Hydrous  aluminum  silicates  of  the  kaolin  group  often  colloidal. 

Colloidal  silicic  acid  yielding  opal,  chalcedony  or  chert. 

Iron  hydroxides  probably  in  colloidal  condition. 

Sericite  (white  muscovite)  from  feldspar. 

Rutile,  possibly  from  titanic  acid  in  colloids. 

//  the  decomposition  is  partial  there  will  be  intermediate  products. 
Albite  and  anorthoclase  from  more  basic  feldspars. 
Chlorite  from  hornblende,  biotite,  pyroxene. 
Epidote  from  feldspar. 

Serpentine  from  chrysolite,  enstatite,  pyroxene,  hornblende. 
Talc  from  pyroxene,  amphibole,  enstatite. 
Magnetite  from  chrysolite,  biotite. 
Amphiboie  from  pyroxene. 

Under  peculiarly  favorable  circumstances  the  silica  may  be  carried 
away,  leaving  bauxite,  gibbsite,  limonite  or  other  hydroxides. 

7.  The  Minerals  of  the  Chemical  Sediments. 

The  deposition  of  minerals  from  weathering  solutions  may  take 
place  from  springs  or  running  streams  or  in  marshes,  lakes,  seas 
or  ocean. 

The  Minerals  Deposited  by  Springs.* 

Although  all  springs  contain  mineral  matter  the  water  is  often 
merely  rain  water  which  has  followed  a  comparatively  short 

*  Clarke  classifies  them  as  chloride  waters,  sulphate  waters,  carbonate  waters, 
silicious  waters,  nitrate,  phosphate  and  borate  waters,  acid  waters.  Bulletin  491, 
U.  S.  Geol.  Survey,  p.  190. 


2  54  MINERAL  OGY. 

course  through  the  soil  and  emerged  at  a  lower  elevation.  It  con- 
tains little  more  than  the  dissolved  gases  from  the  atmosphere. 
Other  springs,  particularly  thermal  springs  and  geysers  with  tem- 
peratures independent  of  the  season  of  the  year,  may  contain 
sufficient  dissolved  material  to  deposit  solids  on  emergence  or 
during  their  passa'ge  underground.  The  principal  deposits  ob- 
tained are: 

Carbonates,  calcite,  aragonite,  siderite,  hydrozincite,  hydro- 
dolomite  (stalactites,  calc  sinter,  tufa,  and  flos  ferri  are  of  this 
type). 

Silica,  opal,  quartz,  chalcedony. 

Sulphides  and  Sulphur,  cinnabar,  realgar,  orpiment,  stibnite, 
galenite,  sulphur. 

Other  Deposits. — Sassolite,  scorodite,  fluorite,  celestite,  the  alums,  halloysite, 
siderite,  and  limonite. 

The  Minerals  Deposited  by  Running  Streams. 

The  dissolved  material  of  rivers  and  streams  consists  essentially 
of  carbonates,  sulphates  and  chlorides  of  calcium,  sodium,  mag- 
nesium and  potassium  and  considerable  silica.  Before  reaching 
the  ocean  most  of  the  silica,  carbonic  acid  and  calcium,  and  about 
half  of  the  potassium  disappear.*  Definite  mineral  deposits  are 
rare;  the  mud  at  the  bottom  is  clay  like.  Sometimes  there  are 
deposits  of  travertine. 

The  Minerals  formed  in  Oceans. 

Some  deposits  of  calcium  carbonate  and  of  dolomite  are  believed 
to  be  chemical  sediments.  Glauconite  forms  just  beyond  the  wave 

*  For  comparison  of  mineral  components  the  general  average  for  river  and  lake 
waters  and  the  mean  of  77  analyses  of  ocean  water  collected  by  Challenger  expedition 
are  here  given:  Bull.  U.  S.  Geol.  Surv.,  491,  p.  106. 

River  and  Lake.  Ocean. 

COs 35-15  2.07 

SO4 12.14  7-6p 

Cl 5-68  55.29 

Br .18 

NO3 90 

Ca 20.39  i. 20 

Mg 3-41  3-72 

Na 5.79  30.59 

K 2.12  i. ii 

(FeAl)203 2.75 

11.67 


FORMATION  AND    OCCURRENCE    OF  MINERALS.      255 

action  and  the  other  important  iron  silicates,  greenalite,  chamosite 
and  thuringite,  are  supposed  to  have  a  similar  origin. 

The  proportion  of  dissolved  solids  in  the  ocean  is  only  33  to  37 
in  the  1,000.  Deep  sea  dredgings  bring  to  light  principally  a  red 
clay  containing  minute  crystals  of  a  rare  zeolite  called  phillipsite, 
nodules  of  hydrated  oxide  of  manganese  and  iron  and  some 
enstatite,  all  apparently  resulting  from  the  decomposition  of  a  lava. 

For  the  dissolved  constituents  to  separate  there  is  needed  a 
concentration  of  the  solution,  usually  a  land-locked  basin  with  a 
shallow  bar  between  it  and  the  sea. 

The  usual  formation  consists  of  beds  of  anhydrite,  gypsum  and 
halite.  After  their  separation  the  mother  liquor  contains  chiefly 
sulphates  and  chlorides  of  potassium  and  magnesium.  These 
usually  escape;  in  fact,  only  one  great  deposit  is  known,  that  of 
Stassfurt  and  Leopoldshalle,  south  of  Magdeburg,  Prussia. 

It  has  been  theorized  that  the  raising  of  the  bar  converted  the 
basin  into  a  salt  lake  from  which  further  evaporation  occurred, 
giving  successively  kieserite,  carnallite  and  by  secondary  reactions 
kainite,  sylvite,  boracite  and  a  series  of  other  species. 

Minerals  formed  in  Lakes. 

In  some  lakes  calcium  minerals  are  rare  and  the  deposits  are 
chiefly  halite  and  other  soda  minerals  such  as  mirabilite,  natron 
and  trona.  In  others  which  have  probably  received  boric  acid 
from  hot  springs  the  boron  minerals  are  prominent  especially 
borax  and  ulexite.  Other  carbonates,  sulphates  and  chlorides  are 
also  present. 

8.  The  Minerals  of  the  Sediments  due  to  Organisms. 

Aragonite  and  Calcite.  By  Action  of  Animals. — Where  marine  life  is  abundant 
CC»2  is  the  principal  gas  in  the  sea  water;  similarly  when  organic  decay  is  in  progress 
ammonium  carbonate  is  formed.  The  shells  and  frameworks  are  in  part  aragonite, 
in  part  calcite. 

By  Action  of  Plants. — Algae  chara,  mosses  and  many  aquatic  plants  absorb  the 
CO2  and  thus  become  coated  with  CaCOs,  forming  sinter  or  travertine,  which  may 
later  be  compacted  by  further  deposition  of  CaCOs.  Fresh  water  marls  also  are  in 
part  due  to  action  of  plants. 

Dolomite.  In  marine  sediments  magnesium  carbonate  tends  to  accumulate,  while 
the  more  soluble  calcium  carbonate  is  dissolved. 

Coral  in  the  living  animal  is  aragonite.  Coral  rock  may  be  essentially  dolomite, 
the  lime  being  removed  and  replaced  by  magnesia  from  the  sea. 

Magnesite. 


256  MINERAL  OGY. 

i 

Ltmonite  (bog  ore)  is  in  part  due  to  one  of  the  algae. 

Silica  taken  from  ocean  water  by  sponges,  radiolaria,  etc.,  forms  banks  of  horn- 
stone.  Diatoms  in  marshes  yield  great  beds  of  soluble  silica.  Algae  in  hot  springs 
precipitate  geyserite. 

Sulphur  is  separated  from  sulphates  by  certain  algae  and  bacteria,  and  by  de- 
composing organic  matter. 

Pyrite,  marcasite  and  some  other  sulphides  are  precipitated  from  solutions  by 
decomposing  organic  matter. 

Phosphates. — The  marine  deposits  of  bone  shell  and  animal  matter  by  relatively 
more  rapid  solution  of  the  carbonates  form  phosphate  nodules  and  by  later  changes 
form  the  large  deposits  of  phosphate. 

Soda  Nitre  and  Nitre  may  be  regarded  as  due  to  nitrifying  organisms. 

D.     METAMORPHIC    MINERALS   AND   VEIN   MINERALS. 

9.  The  Minerals  of  Contacts. 

Contact  metamorphism  occurs  when  an  igneous  rock  penetrates 
another  rock  and  is  a  pneumatolytic  process  involving  heat, 
pressure,  and  the  mineralizing  vapors  given  off  by  the  intrusive 
rock,  chiefly  steam  and  often  fluorine,  boric  acid,  etc.  The  text- 
ures of  both  rocks  change  and  new  minerals  form,  at  the  contact 
and  for  some  distance  from  it. 

The  action  is  largely  a  rearrangement  of  the  same  material  into 
new  compounds  with  little  total  chemical  change.  This  is  most 
marked  in  the  country  rock.  In  the  igneous  rock  the  attempt  of 
the  vapors  to  escape  may  form  the  minerals  of  the  pegmatites 
such  as  tourmaline. 

The  zone  of  contact  will  vary  from  a  few  inches  to  a  mile  in 
width. 

Granite  Contact  with  Limestone. 

An  impure  siliceous  limestone  in  contact  with  an  eruptive  granite 
would  probably  be  converted  into  a  granular  marble*  containing 
crystals  of  silicates,  chiefly  calcium-bearing  but  varying  with  the 
impurities  in  the  limestone. 

Very  characteristic  species  are  garnet  (chiefly  grossularite), 
vesuvianite,  amphibole  (especially  tremolite,  also  actinolite,  horn- 
blende, pargasite),  pyroxenes  (especially  diopside,  also  fassaite), 
wollastonite,  wernerite,  epidote,  biotite,  and  tourmaline  (especially 
brown  varieties). 

Tf  magnesia  is  plentiful  there  may  form:  spinel,  brucite,  and 

*  The  more  silica  present  the  more  CO2  will  be  displaced. 


FORMATION  AND    OCCURRENCE    OF  MINERALS.     257 

the  silicates,  forsterite,  chrysolite,  enstatite,  hypersthene,  and  their 
alterations,  talc  and  serpentine. 

Carbonaceous  material  forms  graphite.  Minor  minerals  are  rutile,  fluorite,  zircon, 
monazite,  lapis  lazuli. 

Contacts  with  Argillaceous  Rocks.     (Clays,  shales  and  slates.) 
Near  the  contact  the  rocks  are  baked  to  a  dense  hornfels  which 

under  the  microscope  may  show  many  minerals;  further  out  this 

grades  into  schists. 

The  most  characteristic  species  are: 

Micas   especially  biotite.     Andalusite   (chiastolite),  frequently 

sillimanite    and    sometimes    cyanite,    staurolite,   tourmaline  and 

iolite.      Amphibole    (hornblende).      Feldspars — anorthite,   albite, 

etc.     Quartz. 

Accessories  are  rutile,  graphite,  spinel,  corundum. 

Contact  metamorphism  will  effect  similar  changes  in  other 
mineral  deposits,  sandstones,  beds  of  anhydrite,  gypsum  or  siderite 
or  even  basic  eruptive  rocks. 

There  may  be  almost  fusion  near  the  intrusive  mass  and  in  such  a  case  the 
metamorphic  minerals  may  pass  back  to  igneous  minerals,  for  instance,  amphibole  to 
chrysolite  and  pyroxene. 

10.  The  Minerals  Formed  in  Regional  Metamorphism. 

The  chemical  changes  due  to  intense  pressure  from  rock  folding, 
circulating  waters  often  hot  and  charged  with  many  constituents 
including  the  so-called  mineralizing  agents  are  very  complex,* 
many  new  minerals  form  often  denserf  than  the  originals  and  many 
with  constitutional  water, J  basic  feldspars  tend  to  form  more 
acid  varieties,  pyroxene  to  change  to  amphibole  and  amphibole 
to  chlorite  or  conversely  micas  and  chlorite  may  form  feldspars 
and  hornblende. 

After  the  crushing  has  ceased,  as  shown  by  the  fact  that  they 
are  not  crushed,  porphyritic  crystals  of  anhydrous  minerals  develop 

*  Clarke  sums  up  the  reactions  producing  chemical  changes  in  metamorphism  as 
molecular  rearrangement,  hydration,  dehydration,  oxidation,  reduction;  other 
changes  by  percolating  solutions,  and  by  gases  and  vapors,  changes  by  igneous 
intrusives. 

t  Largely  molecular  rearrangements  giving  decreased  volume,  e.  g.,  plagioclase 
and  orthoclase  to  albite,  zoisite,  muscovite,  quartz  with  loss  of  15  per  cent,  volume. 

|  Micas,  chlorites,  epidotes,  etc. 
18 


258  MINERALOGY. 

of  higher  density  than  the  average  of  the  rock.  No  simple  list 
can  be  made,  the  material  and  the  reactions  being  too  varied. 

Minerals  often  developed  porphyritically  are  garnet,  staurolite, 
andalusite,  iolite,  albite,  rutile,  tourmaline,  pyroxene,  amphibole, 
ilmenite,  apatite,  magnetite,  topaz,  biotite,  titanite. 

Other  common  or  locally  very  prominent  species  are :  sillimanite, 
cyanite,  the  micas  (phlogopite,  biotite,  muscovite),  other  feldspars, 
the  chlorites,  epidote,  zoisite,  and  piedmontite,  serpentine  and 
talc,  wollastonite,  wernerite,  corundum,  beryl  and  chrysoberyl, 
graphite. 

Important  ore  bodies,  especially*  in  iron,  manganese  and  zinc 
may  be  products  of  metamorphic  action. 

Minor  species  are  vesuvianite,  prehnite,  zircon,  hematite,  monazite,  gibbsite, 
pyrophyllite,  spinel. 

ii.  The  Minerals  of  Veins  and  Replacements. 

In  all  classes  of  rocks  there  are  numerous  fissures  and  cavities 
into  which  the  underground  water  can  penetrate.  Many  of 
these  have  been  rilled  by  minerals  deposited  from  these  waters. 

Veins  strictly  are  tabular  or  sheet-like  masses  rilling  crevices  or 
fissures.  Technically  they  are  called  "mineral  veins"  only  when 
they  contain  ores.  More  irregular  bodies  called  stocks,  beds, 
lenses,  occur  which  may  sometimes  owe  their  shape  to  the  filling 
of  irregular  cavities  but  more  often  to  a  solution  and  replacement 
of  the  original  minerals  of  the  country  rock  (see  p.  246).  Fre- 
quently also  deposits  occur  which  are  not  so  definitely!  connected 
.with  veins  arid  yet  evidently  are  complete  or  partial  replacements 
.of  a  rock  such  as  limestone  by  a  new  mineral. 

i  .  For  instance,  the  Cleveland  oolitic  iron,  ore  is  oolitic  carbonate  of  ,iron  which  has 
replaced  oolitic  limestone;  and  the  manganese  deposits  of  the  Thuringer  Wald  are 
manganese  ores  which  have  replaced  everything  but  the  quartz  of  a  porphyry. 

*  For  instance,  Weinschenk  gives  as  accessories  in  the  crystalline  schists: 

Oxide  ore  bodies,  magnetites  like  Oravitza,  manganese  oxides  like  Langban, 
'manganese  zinc  deposits,  like  Franklin,  magmatic  concentrations  in  gneiss  or  erup- 
tives. 

Sulphide  ore  bodies — pyrrhotite,  pyrite,  chalcopyrite,  sphalerite,  galenite. 

Carbonate  ore  bodies — siderite  usually  in  limestone. 

Emery  in  granular  limestone,  Naxos,  and  in  mica  schist,  Chester,  Mass. 

t  Replacements  are  usually  connected  with  some  channel  or  fissure  through  which 
the  aqueous,  or  gaseous  solutions  may  have  entered.  ,  .  .  , 


FORMATION  AND    OCCURRENCE    OF  MINERALS.      259 

The  minerals  of  veins  by  their  composition  and  arrangement  are 
shown  to  be  deposits  from  solution,  but  in  most  cases  not  simply 
solutions  of  the  neighboring  rocks  in  the  underground  water  but 
also  solutions  in  the  vapors  of  deep-seated  magmas.  Veins  with 
metallic  contents  being  usually  connected  with  some  intrusion  of 
igneous  rock. 

As  the  vapors  rise  into  regions  of  lower  pressure  and  tempera- 
ture condensation  takes  place,  fluid  solutions  form,  various  species 
separate  and  are  deposited  on  the  walls  and  may  ultimately  fill 
the  fissure,  forming  a  vein. 

The  minerals  formed  in  this  way  are  usually  divided  into  ores* 
and  gangue  minerals  and  a  complete  list  would  include  most  of 
the  species  described  in  this  book.  The  following  lists  give  some 
idea  of  relative  frequency. 

Primary  Ores.  The  great  ores  are  pyrite,  galenite,  sphalerite, 
and  chalcopyrite.  These  frequently  carry  valuable  amounts  of 
silver,  gold,  copper,  nickel. 

Common  in  veins  also  are  arsenopyrite,  stibnite,  tetrahedrite, 
chalcocite,  native  gold,  gold  tellurides  (calaverite,  sylvanite,  pet- 
zite,  etc.).  Rich  silver  minerals — argentite,  polybasite,  proustite, 
pyrargyrite,  stephanite. 

Others  are,  smaltite,  cobaltite,  niccolite,  millerite,  braunite,  hausmannite,  rhodo- 
chrosite,  bornite,  enargite,  etc. 

Gangue  Minerals. — The  great  gangue  mineral  is  quartz  (or 
sometimes  the  silica  is  chalcedony  or  opal  or  both)  and  following 
this  are  calcite,  dolomite,  siderite  and  other  carbonates,  fluorite, 
barite. 

Locally  common  fare  rhodonite,  rhodochrosite  and  orthoclase 
(valencianite) ,  roscoelite.  Others  are  zeolites,  chlorite,  axinite,{ 
celestite. 

High  Temperature  Veins. 

Certain  deposits  appear  from  their  minerals  and  the'  changes  in 
the  country  rock  to  have  formed  at  higher  temperatures  and 

*  Ores  are  minerals  containing  desired  elements.  Gangue  minerals  are  all  other 
minerals  in  the  deposit.  The  minerals  formed  from  the  ascending  waters  may  be 
called  primary,  those  formed  later  secondary. 

t  Tonopah,  Nev  ,  Pachuca,  Mex.,  Butte,  Mont.,  Silverton,  CbL  - ' 

J  Kongsberg,  Norway. 


260  MINERAL  OGY. 

pressures  and  with  so  decided  pneumatolytic  action  that  their 
minerals  suggest  those  of  a  pegmatite. 

The  most  important  group  of  these  are  the  tin  veins  which 
grade  into  wolframite  or  molybdenite  veins  and  with  them  Lind- 
gren  classes*  certain  veins  of  gold  quartz  and  gold  telluride 
(Australia)  and  certain  veins  of  copper,  lead  and  cobalt  character- 
ized by  association  with  tourmaline. 

The  characterizing  gangue  minerals  of  such  deposits  are : 
Tourmaline,  biotite,  garnet,  fluorite,  topaz,  pyroxene,  amphi- 
bole,  apatite,  ilmenite,  magnetite,  mica,  spinel,  feldspar  (usually 
albite),  lithia  mica. 

The  ore  minerals  of  tin  veins  are  fairly  constant  and  include  cassiterite,  molybdenite, 
wolframite,  scheelite,  bismuth,  bismuthinite,  arsenopyrite  and  minor  amounts  of 
the  common  sulphides,  pyrite,  pyrrhotite,  chalcopyrite,  galenite,  sphalerite. 

Secondary  Vein  Minerals. 

Veins,  like  the  rock  in  which  they  occur,  undergo  changes. 
Near  the  surface  there  is  oxidation  and  solution,  lower  the  solu- 
tions may  yield  up  their  contents,  forming  an  economically  very 
important  "zone  of  secondary  enrichment,"  below  this  again 
will  be  the  unaltered  ore,  often  very  much  poorer  in  the  desired 
constituent  than  the  enriched  zone  above  it. 

Important  secondary  ores  are: 

Iron.  Limonite  (often  forming  the  principal  metallic  mineral 
in  the  upper  part  of  a  vein),  hematite,  vivianite. 

Silver.  Rich  silver  minerals  as  secondary  enrichments  and 
native  silver,  cerargyrite,  bromyrite,  embolite,  iodyrite  in  the 
upper  portions. 

Copper.  Chalcocite,  covellite,  cuprite  and  bornite  as  secondary 
enrichments,  malachite,  azurite,  copper,  chrysocolla,  chalcanthite, 
brochantite  in  upper  portions, 

Gold.  Native  gold  both  as  secondary  enrichment  and  in  upper 
portions. 

Lead.  Cerussite,  anglesite,  pyromorphite,  mimetite,  crocoite, 
vanadinite,  wulfenite. 

Zinc.     Smithsonite,  calamine. 

*  "Mineral  Deposits,"  611. 


CHAPTER  XVIII. 
THE  MINERALS  OF  METALLIFEROUS  ORE  DEPOSITS. 

The  order*  in  which  the  minerals  are  described  is  chiefly  based 
on  their  economic  uses  as  in  the  former  editions  but  more  groups 
have  been  made,  each  group  consisting  of  the  chief  minerals 
containing  some  economically  important  element,  its  ores  and 
possible  ores,  and  the  more  common  alteration  products. 

To  place  each  group  in  its  right  perspective  its  economic  and 
genetic  relations  are  discussed  under  the  headings  Economic 
Importance  and  Formation  and  Occurrence.  These  group  dis- 
cussions are  followed  by  the  descriptions  of  species. 

In  discussing  formation  and  occurrence  four  great  groups*  of 
deposit  are  usually  made. 

I.  Magmatic  segregations,  p.  251. 
II.  Contact  deposits,  p.  256. 

III.  Veins  and  replacements,  p.  258. 

IV.  Sedimentary  deposits,  p.  252,  including  placers,  residual  de- 

posits, chemical  sediments  and  some  deposits  of  doubtful 
genesis. 

In  descriptions  where  possible  details  previously  given  under  the 
descriptions  of  these  occurrences  will  be  omitted. 

THE   IRON   MINERALS. 

The  minerals  described  are: 


Metal 

Iron 

Fe 

Sulphides 

Pyrrhotite 

FCnSn+l 

Hexagonal 

Pyrite 

FeS2 

Isometric 

Marcasite 

FeS2 

Orthorhombic 

Oxides 

Magnetite 

Fe304 

Isometric 

Hematite 

Fe203 

Hexagonal 

Ilmenite 

FeTiOs 

•• 

Hydroxides 

Turgite 

Fe405(OH)2 

Goethite 

FeO(OH) 

Orthorhombic 

Limonite 

Fe2(OH)6.Fe2O3 

Sulphates 

Copiapite 

Fe2(FeOH)2(S04)5  +  i8H2O 

Monoclinic 

Melanterite 

FeS04  +  7H20 

*  "  Beyschlag 

Vogt  and  Krusch." 

Truscott's  translation,  Vol.  i, 

p.  240. 

261 

262  MINERALOG  Y. 

Phosphate  Vivianite  Fe3(PO4)2  +~8H2O  Monoclinic 

Carbonate  Siderite  FeCOs  Hexagonal 

Silicates  Chamosite  Hydrous  iron  aluminum  silicate 

Thuringite  " 

Other  iron  minerals  elsewhere  described  are  arsenopyrite,  frank- 
linite,  chromite,  columbite,  wolframite,  fayalite,  as  well  as  -many 
iron-rich  varieties  of  pyroxene,  amphibole,  garnet,  mica,  etc. 

ECONOMIC   IMPORTANCE. 

The  iron  minerals  have  important  and  varied  uses,  which  may 
briefly  be  described  under  the  following  heads: 

I.  In  natural  state. 
II.  As  ores  of  iron. 
III.  As  ores  of  sulphur  and  iron. 

I.  Uses  in  Natural  State. 

In  1914  the  production  of  ocher,  umber  and  sienna  and  natural 
oxide  paints  was  51,495  short  tons.*  Limonite  and  hematite  are 
the  principal  natural  oxides  ground  for  paint. 

II.  Minerals  Used  as  Ores  of  Iron. 

In  the  United  States  the  minerals  smelted  for  iron  are,  in  order 
of  quantity  used,f  hematite,  limonite,  magnetite,  and  siderite. 
Goethite  and  turgite  are  commercially  included  with  limonite 
under  the  name  brown  hematite,  and  some  ilmenite  is  smelted 
with  other  ores.  The  residues  from  the  roasting  of  pyrites  are 
sometimes  used  as  a  source  of  iron. 

In  1915  the  United  States  produced  58,843,804!  long  tons  of 
iron  ore,  about  four  fifths  of  which  came  from  the  Lake  Superior 
region  of  Michigan,  Wisconsin  and  Minnesota,  and  about  one 
eighth  came  from  the  Southern  States. 

The  greater  portion  of  the  iron  ore  mined  in  the  world  each  year 
is  converted  into  pig  iron.  That  is,  the  ore  is  deprived  of  its  oxy- 
gen by  the  action  of  incandescent  carbon  and  the  hot  reducing 

*  Mineral  Resources  U.  S. 

t  Ernest  F.  Burchard,  in  Mineral  Resources  of  United  States,  1914,  gives  as  amounts 
mined  for  1914:  Hematite,  38,286,670  long  tons;  limonite' and  goethite,  1,537,750 
long  tons;  magnetite,  1,610,203  long  tons;  siderite,  5,138- long' tons.  The  total 
production  for  1914  being  one-third  less  than  either  1913  or  1915. 

{  Engineering  and  Mining  Journal,  1916. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.     263 

gases  resulting  from  its  combustion,  and  becomes  a  liquid  mass  of 
metallic  iron,  combined  and  mixed  with  a  little  carbon,  silicon, 
phosphorus,  sulphur  and  other  impurities.  The  furnace  used  is  a 
vertical  shaft,  everywhere  circular  in  horizontal  section,  but  usually 
widening  from  the  top  downwards  to  a  certain  level,  and  then 
again  narrowing  to  the  hearth.  Hot  air  is  forced  into  the  furnace 
through  nozzles  called  tuyeres,  entering  just  above  the  hearth. 

The  ore  and  fuel  are  analyzed  and  some  flux  is  added,  which, 
when  combined  with  the  ash  of  the  fuel  and  the  foreign  ingredi- 
ents of  the  ore,  forms  a  definite  silicate  of  known  fusibility,  called 
the  slag.  The  temperature  of  the  furnace  differs  at  different  levels, 
but  is  practically  the  same  at  all  times  at  any  one  level. 

The  ore,  charged  at  the  top,  in  alternate  layers  with  fuel  and 
flux,  passes  through  zones  of  different  temperature  as  it  descends, 
and  is  reduced,  carburized,  fused,  and  flows  into  the  hearth.  The 
slag  forms  in  a  definite  zone  after  the  complete  reduction  of  the 
iron,  and  falls  also  to  the  hearth,  but,  being  lighter,  floats  on  the 
melted  iron  until  drawn  off.  From  time  to  time  the  metal  is  run 
out  into  sand  moulds,  forming  the  pigs  or  pig  iron,  of  which  29,- 
971,191*  long  tons  were  produced  in  the  United  States  in  1915. 

This  pig  iron,  by  various  processes,  is  converted  into  wrought 
iron,  cast  iron  and  steel. 

III.  Minerals  Used  as  Ores  of  Sulphur  and  Iron. 

Pyrite,  and,  to  a  less  extent,  marcasite  and  pyrrhotite,  are  very 
extensively  used  in  the  manufacture  of  sulphuric  acid.  In  1914, f 
1,363,279  tons  were  so  used  in  the  United  States,  of  which  336,662 
were  domestic,  1,026,617  imported.  The  sulphides  are  burned  in 
furnaces  with  grates,  and  the  gases  are  converted  into  sulphuric 
acid.  The  residues,  in  addition  to  iron,  frequently  contain  copper,) 
nickel  or  gold,  which  are  extracted  later. 

FORMATION   AND    OCCURRENCE   OF   THE    MINERALS    OF  IRON. 
The  iron  minerals  occur  in  all  four  classes  of  deposit. 
Magrnatic  Segregation. 

Titaniferous  magrietite%  and  ilmenite,  in  basic  rocks. 

*  Loc.  cit. 

f  Mineral  Industry,  1914,  p.  692. 

J  In.  many  cases  this  is  a  microscopic  mixture  of  pure  magnetite  and  ilmenite 
which  may  be  separated  by  magnetic  concentration.  Beyschlag  Vogt  and  Krusch, 
p.  254. 


264  MINERAL  OGY. 

As  at  Ekersund-Soggendal,  Norway;  Taberg,  Sweden ;  Saguenay 
River  and  St.  Paul's  Bay,  Canada;  and  Elizabeth  town  and  Sand- 
ford  Lake,  Adirondacks,  N.  Y. 

Magnetite  from  acid  magmas  with  some  hematite,  both  free  from 
titanium. 

This  includes  the  enormous  Swedish  magnetite  deposits  such  as 
Kiirunavaara,  Gellivare,  etc.,  and  others  in  Norway. 

Pyrrhotite  in  the  nickel-pyrrhotite  deposits  of  Canada,  Norway, 
Sweden  and  Piedmont  pyrite  sometimes  being  prominent. 

Pyrite  in  the  great  intrusive  pyritic  deposits,  such  as  Rio  Tinto, 
Spain;  Agordo,  Italy;  Bodenmais,  Bavaria;  Sain  Bel,  France. 
Possibly  Fahlun,  Sweden.  Some  authorities*  regard  the  great- 
est of  these  to  be  magmatic  segregations. 

Contact  Deposits. 

Hematite  of  Elba  and  the  magnetite  and  hematite  of  Christiania, 
Sweden;  Banat,  Hungary;  and  "practically  every  known  iron 
deposit  along  the  Pacific  coast  from  Alaska  to  southern  Chili. "f 

Pyrrhotite  and  pyrite  as  at  Traversella,  Piedmont;  Ducktown, 
Tenn.J 

Veins. 

Pyrite,  marcasite,  pyrrhotite  and  siderite  all  occur  as  vein  min- 
erals, pyrite  much  more  frequently  than  the  others. 

Replacements. 

Limonite  replacing  limestone  is  common  along  the  Appalachian 
Mountains  and  extensively  mined  in  the  Southern  States. 

Hematite  is  often  a  replacement  of  limestone  as  at  the  great 
deposit  of  Ulverstone,  Lancashire.  The  most  important  ex- 
amples, are  the  great  Lake  Superior  deposits§  which  consist 
chiefly  of  hematite  but  also  goethite  and  turgite  and  are  be- 

*  Beyschlag,  Vogt  and  Krusch.     Truscott  translation,  p.  301, 

f  Eckel,  "Iron  Ores,"  p.  87. 

J  Lindgren,  "Mineral  Deposits,"  p.  598. 

§  "  As  first  deposited  the  iron  formation  consisted  of  iron  carbonate  or  ferrous 
silicate  (grenalite)  with  some  ferric  oxide  all  minutely  interlayered  with  chert  form- 
ing the  ferruginous  chert.  When  these  were  exposed  to  weathering  the  ferrous 
compounds,  the  siderite  and  greenalite,  oxidized  to  hematite  and  limonite  essentially 
in  siiu,  although  some  of  it  was  simultaneously  carried  away  and  redeposited.  The 
result  was  ferruginous  chert  or  jasper,  averaging  less  than  30  per  cent,  of  iron. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.     265 

lieved  to  have  formed  by  weathering  of  lean  silicates  and 
carbonates  of  sedimentary  origin  and  subsequent  replacement 
of  silica. 

Siderite  deposits  formed  by  replacement  of  limestone  exist  in 
Cornwall,  the  Alps  and  Bohemia. 

Sediments. 

Magnetite  (black  sands) ,  or  ilmenite  (iserite) . — Transported  con- 
centrates. 

Limonite  or  siderite. — Bog  deposits  largely  precipitated  by  iron 
bacteria. 

If  much  carbonic  acid  or  decaying  organic  matter  is  present 
the  bog  ore  formed  is  siderite.  If  air  has  free  access  the  bog 
ore  is  limonite. 

Hematite,  limonite,  siderite  and  the  silicates  chamosite  and  thur- 
ingite.  "  Marine  Basin  Ores"  as  deposited  in  sea  basins,  usually 
oolitic.  The  Clinton  oolitic  ores  are  typical. 

Pyrite,  pyrrhotite  and  marcasite  disseminated  or  in  concretions 
in  limestone,  clay,  marl  and  coal  as  at  Meggen  and  Rammelsberg, 
Germany. 

Residual. 

Limonite,  goethite,  etc.,  left  after  weathering,  p.  247,  sometimes 
hematite  and  colloidal  mixtures.  The  Appalachian  ores  and  the 
ores  of  Cuba  are  types.  Limonite,  formed  chiefly  by  alteration  of 
pyrite  and  pyrrhotite.  The  most  important  Gossan  deposits  are 
in  Ducktown  District,  Tenn.,  and  Great  Gossan  Lead,  Va. 

IRON. 

COMPOSITION. — Fe  with  some  Ni,  Cr,  Co,  Mn. 

GENERAL  DESCRIPTION. — Masses  and  imbedded  particles  of  white  to  gray  metal, 
resembling  manufactured  iron. 

CRYSTALLIZATION. — Isometric,  several  meteoric  irons  showing  minute  cubes  and 
cubes  modified  by  {m}  and  {no}.  Some  meteorites,  especially  the  Braunau,  are 
single  crystals  the  same  cubic  cleavage  planes  extending  through  the  entire  lump. 
Etching  frequently  develops  the  crystalline  structure  as  lines  or  bands  at  60°  or  90° 
which  are  in  part  due  to  plates  of  varying  composition  and  in  part  to  parting  planes 
parallel  to  {211}. 

PHYSICAL  CHARACTERS. — Opaque.     Lustre,  metallic.     Color,  steel-gray  to  iron- 

The  concentration  of  the  iron  to  50  per  cent,  and  over  has  been  accomplished 
essentially  by  the  leaching  of  the  silica  bands  from  the  chert  and  jasper."  C.  K. 
Leith,  Economic  Geology,  Vol.  3,  p.  276. 


266  MINER  A  LOGY. 

black.  Streak,  metallic  gray.  H.,  4  to  5.  Sp.  gr.,  7.3  to  7.8.  Strongly  attracted 
by  the  magnet.  Tough  and  malleable.  Fracture,  hackly. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  Soluble  in  acids.  In  borax  or  salt  of  phos- 
phorus, reacts  only  for  iron. 

REMARKS. — Iron  is  found  sparingly  in  eruptive  rocks,  especially  basalts,  usually 
in  minute  grains  as  at  Antrim,  Ireland,  and  in  the  trap  rocks  of  New  Jersey  and  the 
dolerite  of  Mt.  Washington,  N.  H.  Masses  up  to  the  size  of  a  walnut  are  found  in 
the  basalt  of  Aschenhiibel,  Saxony,  and  masses,  one  of  which  weighed  fifty  thousand 
pounds,  have  weathered,  from  the  basalt  of  Ovifak,  Disco  Island,  Greenland. 

Iron  occurs  at  Chotzen,  Bohemia,  apparently  as  the  result  of  the  reduction  of 
limonite,  and  most  meteorites  are  either  alloys  of  iron  and  nickel  or  contain  such 
alloys. 

PYRRHOTITE.— Magnetic  Pyrites,  Mundic. 

COMPOSITION.— FenSn  +  x.  Fe6S7  to  FenS12,  with  frequently  small 
percentages  of  cobalt  or  nickel. 

GENERAL  DESCRIPTION. — Usually  a  massive  bronze  metallic  min- 
eral, which  is  attracted  by  the  magnet  and  can  be  scratched  with 
a  knife.  Sometimes  occurs  in  tabular  hexagonal  crystals. 

Physical  Characters.     H.,  3.5  to  4.5.     Sp.  gr.,  4.5  to  4.6. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  grayish-black.  TENACITY,  brittle. 

COLOR,  bronze-yellow  to  bronze-red,  but  subject  to  tarnish. 
Attracted  by  the  magnet. 

BEFORE  BLOWPIPE,  ETC. — Fuses  readily  on  charcoal  to  a  black 
magnetic  mass,  evolves  fumes  of  sulphur  dioxide,  but  does  not  take 
fire.  In  closed  tube,  yields  a  little  sulphur.  In  open  tube,  gives 
fumes  of  sulphur  dioxide.  Soluble  in  hydrochloric  acid,  with 
evolution  of  hydrogen  sulphide  and  residue  of  sulphur. 

SIMILAR  SPECIES. — Pyrrhotite  resembles  pyrite,  bornite  and  nic- 
colite  at  times,  but  differs  in  being  attracted  by  the  magnet  and  by 
its  bronze  color  on  fresh  fracture. 

REMARKS. — The  most  important  deposit  is  that  at  Sudbury,  Canada.  Others  are 
Kongsberg,  Norway;  Andreasberg,  Harz;  Ducktown,  Tenn.,  Piilaski,  Va.;  Straff ord 
and  Ely,  Vt.;  Lancaster  Gap"; 'Pa.  Smaller  beds  "are  common. 

PYRITE.— Iron  Pyrites,  Fool's  Gold. 

COMPOSITION.— FeS2  (Fe  46.7,  S  53.3  per  cent.),  often  contain- 
ing small  amounts  of  Cu,  As,  Ni,  Co,  Au.v 

GENERAL  DESCRIPTION. — A  brass -colored,  metallic  mineral, 
frequently  in  cubic,  or  .other  isometric,  crystals. or  in  crystalline 
masses,  which  may  be  any  shape,  as  botryoidal,  globular,  .stalac- 
titic,  etc.  Less  frequently  in  non-crystalline  masses. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.     267 
FIG.  312.  FIG.  313.  FIG.  314. 


FIG.  316. 


FIG.  317. 


FIG.  318. 


FIG.  319. 


FIG.  320. 


CRYSTALLIZATION.  —  Isometric,  class  of  diploid,  p.  65.  Most 
common  forms  are  cube  a,  Fig.  312,  and  pyritohedron  ^,  Fig.  313, 
a :  2a :  co  a  ;  { 2 10}  or  combinations  of  these,  Fig.  315.  The  octa- 
hedron also  occurs  alone,  Fig.  314,  or  in  combination  with  a  and 
€,  Figs.  316,  317,  318,  and  the  diploid  5  =  (a  :  fa  :  30);  {321}  is 
not  rare  in  combinations,  Fig.  319^  320. 

The  faces  of  the  cube  and  pyritohedron  are  frequently  striated 
in  one  direction  parallel  to  intersections  of  these  two  forms. 

Physical  Characters.     H.,  6  to  6.5.     Sp.  gr.,  4.9^0  5.2. 
LUSTER,  metallic.  OPAQUE. 

STREAK,  greenish-black.  TENACITY,  brittle. 

COLOR,  pale  to  full  brass-yellow  and  brown  from  tarnish. 
BEFORE  BLOWPIPE,  ETC. — On  charcoal,  takes  fire  and  burns  with 
a  blue  flame,  giving  off  fumes  of  sulphur  dioxide,  and  leaving  a 


268  MINERAL  OGY. 

magnetic  residue  which,  like  pyrrhotite,  dissolves  in  hydrochloric 
acid  with  evolution  of  hydrogen  sulphide.  In  closed  tube,  gives  a 
sulphur  deposit.  Insoluble  in  hydrochloric  acid,  but  soluble  in 
nitric  acid  with  separation  of  sulphur. 

SIMILAR  SPECIES. — Pyrite  is  harder  than  chalcopyrite,  pyrrho- 
tite, or  gold.  It  differs  from  gold,  also,  in  color,  streak,  and  brit- 
tleness.  It  differs  from  marcasite  .  chiefly  in  the  fact  that  its 
sulphur  is  more  oxidized  by  the  same  treatment;  for  instance, 
pyrite  in  very  fine  powder  is  completely  dissolved  in  about  its  own 
bulk  of  strong  nitric  acid  whereas  marcasite  leaves  some  separated 
sulphur;  or  if  boiled  with  a  solution  of  ferric  sulphate  about  52 
per  cent,  of  the  sulphur  of  pyrite  is  dissolved  and  about  12  per 
cent,  of  the  sulphur  of  marcasite. 

REMARKS. — The  uses  and  occurrence  are  described  p.  263.  The  most  cele- 
brated locality  is  the  Rio  Tinto  region,  in  Spain,  from  which  immense  quantities 
of  a  gold-  and  copper-bearing  pyrite  are  annually  procured.  Norway  and  Ger- 
many are  large  producers.  The  largest  deposits  worked  in  the  United  States 
are  in  Virginia,  New  York  and  California.  In  compact  specimens  it  is  not  easily 
altered,  but  granular  masses  readily  oxidize  and  are  decomposed,  forming  sulphate 
of  iron  and  sulphuric  acid,  thus  acting  as  a  vigorous  agent  in  the  decomposition  of 
rocks.  The  final  results  are  usually  limonite  and  sulphates  of  calcium,  sodium, 
magnesium,  etc. 

MARCASITE— White  Iron  Pyrites. 

COMPOSITION. — FeS2,  as  in  pyrite. 

GENERAL  DESCRIPTION. — Ferric  sulphide  is  dimorphous.  Mar- 
casite differs  from  pyrite  in  crystalline  form,  and  in  little  else. 
It  occurs  in  orthorhombic  forms,  and  in  crystalline  masses.  The 
compound  crystals  have  given  rise  to  such  names  as  cockscomb 

FIG.  321.  FIG.  323. 


FIG.  322. 

pyrites,  spear  pyrites,  etc.,  from  their  resemblance  to  these  objects. 
Often,  with  radiated  structure.  Color  on  fresh  fracture  is  usually 
whiter  than  in  pyrite. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.     269 

FIG.  324. 


Marcasite  Twin  Crystal.     After  Lacroix. 


0.7662:  i :  1.2342. 


CRYSTALLIZATION. —  Orthorhombic,  a :  1 :  c 
Crystals  usually  tabular  parallel  to  base. 

Simple  forms  show  unit  prism  m,  basal  pinacoid  c  and  often  one 
or  more  brachy  domes  as  g=  (oo^:  b\  \c)  ;  {013}.  Compound 
"fivelings"  with  twin  plane  m,  Figs.  323  and  324,  are  frequent. 

Supplement  angles  are  mm  =  74°  55',  cg=  22°  21 ', 

Physical  Characters.     H.,  6  to  6.5.     Sp.  gr.,  4.6  to  4.9. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  nearly  black.  TENACITY,  brittle. 

COLOR,  pale  brass-yellow,  darker  after  exposure. 

BEFORE  BLOWPIPE,  ETC.     As  for  pyrite. 

SIMILAR  SPECIES. — As  for  pyrite,  from  which  it  is  only  dis- 
tinguishable by  crystalline  form,  cleavage,  and  by  the  slighter 
effect  of  oxidizing  agents  (see  pyrite) . 

REMARKS. — Marcasite  is  more  readily  decomposed  than  pyrite,  and  is,  therefore, 
an  even  less  desirable  constituent  in  building  material,  etc.  It  is  found  at  Cumming- 
ton,  Mass.;  Warwick,  N.  Y.;  Joplin,  Mo.;  Haverhill,  N.  H.;  and  in  many  other 
localities  and  is  usually  mistaken  for  pyrite. 

Well-known  foreign  localities  are  the  chalk  marls  near  Dover,  England,  the  clay 
beds  near  Carlsbad.  The  Wilkinson  Mine  of  Wisconsin  yields  it  in  commercial 
quantities. 


270 


MINERALOGY. 


THE    SULPHATES    OF   IRON. 

Decomposing  sulphides  form  sulphates  which  in  dry  regions 
may  persist  but  oftener  are  dissolved  and  lost.  There  are  a  large 
series  of  these  of  which  the  best  known  are 

MELANTERITE. — Copperas,  FeSO4  +  yH2O.  A  pale  green  fibrous  efflorescence 
on  pyrite  or  marcasite,  or  stalactite  massive  or  pulverulent.  It  has  a  sweet  astringent 
taste  and  on  exposure  it  becomes  dull  yellowish-white. 

Found  at  Copperas  Mt.,  Ohio;  Goslar,  Hartz;  and  many  other  localities. 

COQUIMBITE.  Fe2(SO4)3  +  9H2O.  Violet  to  white  or  greenish-glassy  material 
often  with  hexagonal  crystals  with  an  astringent  taste,  often  coated  with  copiapite. 

Found  as  a  large  bed  in  trachyte  rock  at  Tierra  Amarilla,  Atacama,  Chili. 

COPIAPITE.— Misy,  Fe2(FeOH)2(SO4)5  +  i8H2O,  often  with  some  A12O3  or  MgO. 
Brownish-yellow  to  sulphur-yellow,  granular,  or  in  loosely  compacted  crystalline 
scales,  with  a  disagreeable  metallic  taste. 

Found  with  coquimbite,  also  in  New  Mexico,  California,  and  elsewhere. 

For  all  three  the  tests  are  essentially  alike.  H.,  2  to  3,  sp.  gr.,  1.8  to  2.1.  Tastes 
as  stated.  On  charcoal,  fuse  and  become  magnetic.  Yield  water  inclosed  tube 
and  some  sulphuric  acid.  Soluble  in  water,  giving  the  solution  a  reaction  for 
sulphuric  acid. 

MAGNETITE.— Lodestone,  Magnetic  Iron  Ore. 

COMPOSITION. — Fe3O4  (Fe,  72.4  per  cent.)  often  contains  Ti,  Mg. 

GENERAL  DESCRIPTION. —A  black  mineral  with  black  streak  and 
metallic  lustre,  strongly  attracted  by  the  magnet  and  occurring  in 
all  conditions  from  loose  sand  to  compact  coarse  or  fine  grained 
masses. 

CRYSTALLISATION. — Isometric,  usually  octahedra,  Fig.  325,  or 
loosely  coherent  masses  of  imperfect  crystals.  Sometimes  the 


FIG.  325. 


FIG.  326. 


FIG.  327. 


dodecahedron  d,  Fig.  326,  or  a  combination  of  these,  Fig.  152, 
or  more  rarely  with  the  angles  modified  by  the  trapezohedron 
o  =  (a  :T>a  :  30) ;  {311}.  Fig.  327. 

Twinning  parallel  to  an  octahedral  face  occurs,  sometimes  shown 
by  striations  upon  the  octahedral  faces. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.     271 

Physical  Characters.     H.,  5.5  to  6.5.     Sp.  gr.,  4.9  to  5.2. 

LUSTRE,  metallic  to  submetallic.  f  OPAQUE. 

COLOR  and  STREAK,  black.  TENACITY,  brittle. 

Strongly  attracted  by  magnet  and  sometimes  itself  a  magnet 
(lodestone).  Breaks  parallel  to  octahedron. 

BEFORE  BLOWPIPE,  ETC. — Fusible  with  difficulty  in  the  reduc- 
ing flame.  Soluble  in  powder  in  hydrochloric  but  not  in  nitric 
acid. 

SIMILAR  SPECIES':— No  other  black  mineral  is  strongly  attracted 
by  the  magnet. 

REMARKS. — The  occurrences  are  described,'  p.   263. 

In  this  country  it  is  obtained  from  Pennsylvania,  New  York,  New  Jersey  and 
Michigan.  Lodestones  are  obtained  mainly  from  Magnet  Cove,  Ark. 

HEMATITE.— Specular  Iron,  Red  Iron  Ore. 

COMPOSITION. — Fe2O3,  (Fe  70  per  cent.),  often  with  SiO2,  MgO, 
etc.,  as  impurities. 

GENERAL  DESCRIPTION. — Occurs  in  masses  varying  from  bril- 
liant black  metallic  to  blackish  red  and  brick  red  with  little  luster. 
The  black  is  frequently  crystallized,  usually  in  thin  tabular  crys- 
tals set  on  edge  in  parallel  position,  less  frequently  in  larger  highly 
modified  forms  and  finally  in  scale-like  to  micaceous  masses.  The 
red  varieties  vary  from  compact  columnar,  radiated  and  kidney- 
shaped  masses  to  loose  earthy  red  material.  In  all  varieties  the 
streak  is  red. 

CRYSTALLIZATION.  —  Hexagonal,  scalenohedral  class,  p.  48. 
Axis  c  =  1.365. 

The  most  common  forms  on  the  Elba  crystals  are  the  unit 
rhombohedron  /  and  the  scalenohedron  n  s=  (20.  :  2a  :  a  :  ^c)  ; 
{2243}.  The  rhombohedron  g  =  (a  :  co  a  :  a  :  \c  ;  { io?4}  also 

FIG.  328.  FIG.  329.  FIG.  330. 


272 


MINERALOGY. 


occurs.     Thin  plate-like  crystals  are  the  rule  at  other  localities. 

Sometimes  grouped  in  rosettes,  as  in  the  "  Eisenrosen,"  Fig.  331 

Supplement  angles,  —pp  =  94°  ;  nn  =  5 1  °  59' ;  cp  =  57°  37' ; 


gg 


37°  2' 


en 


61°   13'. 


FIG.  331- 


FIG.  332. 


Eisenrosen,  Fibia  Switz. 


Radiated  r en i form,  Geikie. 


Physical  Characters.     H.,  5.5  to  6.5.     Sp.  gr.,  4.9  to  5.3. 

LUSTRE,  metallic  to  dull.  OPAQUE. 

STREAK,  brownish  red  to  cherry  red.  TENACITY,  brittle  un- 

COLOR,  iron  black, blackish  red  to  cherry  red.  less  micaceous. 

Sometimes  slightly  magnetic. 

BEFORE  BLOWPIPE,  ETC. — Infusible.     Becomes  magnetic  in  re- 
ducing flame.     Soluble  in  hot  hydrochloric  acid.     In  borax  reacts 
for  iron. 
VARIETIES. 

Specular  Iron. — Brilliant  micaceous  or  in  crystals.  Black  in 
color. 

Red  Hematite. — Submetallic  to  dull,  massive,  blackish  red  to 
brownish  red  in  color. 

Red  Ochre. — Earthy  impure  hematite  usually  with  clay.  Often 
pulverulent. 

Clay  Ironstone. — Hard  compact  red  material  mixed  with  much 
clay  or  sand. 

Martite. — Octahedral  crystals,  probably  pseudomorphs. 

SIMILAR  SPECIES. — Resembles  at  times  the  other  iron-ores  and 
massive  cuprite.  It  is  distinguished  by  its  streak  and  strong  mag- 
netism after  heating  in  reducing  flame. 

REMARKS.— As  described  on  p.  264,  the  greatest  hematite  deposit  is  due  to  con- 
centration and  replacement  and  other  great  deposits  to  contact  deposits  and  marine 
oolitic  ores  while  relatively  small  amounts  are  due  to  magmatic  segregation.  By 
far  the  larger  part  is  obtained  from  the  Marquette  and  Gobegic  ranges  of  Michigan 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.     273 

and  from  the  Mesabi  range  in  Minnesota.     Smaller  but  by  no  means  inconsiderable 
amounts  are  mined  in  Alabama  and  other  states. 

ILMENITE. — Menaccanite,  Titanic  Iron-Ore. 
COMPOSITION. — FeTiO3,   sometimes  containing  small  amounts 
of  Mg  or  Mn. 

FIG.  333.  FIG.  334. 


GENERAL  DESCRIPTION. — An  iron-black  mineral,  usually  mas- 
sive or  in  thin  plates  or  imbedded  grains  or  as  sand.  Also,  in 
crystals  closely  like  those  of  hematite  in  angle. 

CRYSTALLIZATION.  —  Hexagonal.  Class  of  third  order  rhom- 
bohedron,  p.  54.  Axis  c  =  1.385.  Usually  thick  plates  showing 
basal  pinacoid  c,  unit  prism  m  and  unit  rhombohedron  p,  Fig.  334, 
or  without  the  prism,  Fig.  333.  Supplement  angles  pp  =  94°  29'; 
^=57°  58'. 

Physical  Characters.— H,,  5  to  6.  Sp.  gr.,  4.5  to  5. 
LUSTRE,  submetallic.  OPAQUE. 

STREAK,  black  to  brownish-red.  TENACITY,  brittle. 

COLOR,  iron-black,  Slightly  magnetic. 

BEFORE  BLOWPIPE,  ETC. — Infusible  in  oxidizing  flame ;  slightly 
fusible  in  reducing  flame.  In  salt  of  phosphorus  gives  a  red  bead 
which,  on  treatment  in  reducing  flame  becomes  violet,  slowly 
soluble  in  hydrochloric  acid  and  the  solution  boiled  with  tin  is 
violet  and  on  evaporation  becomes  rose-red. 

SIMILAR  SPECIES. — Differs  from  magnetite  and  hematite  in  the 
titanium  reactions. 

REMARKS. — As  described  on  p.  263,  it  occurs  as  magmatic  segregations  from 
basic  rocks,  also  as  crystals  and  grains  in  igneous  rocks  and  schists  and  as  sand. 

USES. — It  has  been  used  as  a  constituent  of  the  lining  of  puddling 
furnaces  and  in  the  making  of  ferrotitanum. 

GOETHITE. 

COMPOSITION. — FeO(OH).     Fe,  62.9  per  cent. 

GENERAL  DESCRIPTION. — A  yellow,  red  or  brown  mineral,  occurring  in  small,  dis- 
tinct, prismatic  crystals  (orthorhombic),  often  flattened  like  scales,  or  needle-like,  or 
19 


274 


MINERALOGY. 


grouped  in  parallel  position.  These  shade  into  feather-like  and  velvety  crusts.  Oc- 
curs also  massive  like  yellow  ochre. 

PHYSICAL  CHARACTERS. — Opaque  to  translucent.  Lustre,  adamantine  to  dull. 
Color,  yellow,  reddish,  dark-brown  and  nearly  black.  Streak,  yellow  or  brownish- 
yellow.  H.,  5  to  5.5.  Sp.  gr.,  4  to  4.4. 

BEFORE  BLOWPIPE,  ETC. — Fuses  in  thin  splinters  to  a  black  magnetic  slag.  In 
closed  tube  yields  water.  Frequently  reacts  for  manganese.  Soluble  in  hydrochloric 
acid. 

USES. — Goethite  is  an  ore  of  iron,  but  is  commercially  classed  with  limonite  under 
the  name  of  brown  hematite.  Large  ocherous  deposits  in  Minnesota. 

TURGITE. — Hydrohematite. 

COMPOSITION. — Fe4O5(OH)2,  Fe  =  66.2  per  cent. 

GENERAL  DESCRIPTION. — Nearly  black,  botryoidal  masses  and  crusts  resembling 
limonite  but  with  a  red  streak  and  often  with  a  fibrous  and  satin-like  appearance  on 
fracture.  Also  bright  red  earthy  masses.  Usually  associated  with  limonite  or 
hematite. 

PHYSICAL  CHARACTERS.  —  Opaque.  Lustre,  submetallic  to  dull.  Color,  dark  red- 
dish-black in  compact  form,  to  bright  red  in  ocherous  variety.  Streak,  brownish  red. 
H.,  5.5-6.  Sp.  Or.,  4.29-4.68. 

BEFORE  BLOWPIPE,  ETC.  —  Decrepitates  violently,  turns  black  and  becomes  mag- 
netic. Yields  water  in  closed  tube  with  violent  decrepitation. 

SIMILAR  SPECIES.  —  Is  distinguished  from  limonite  and  hematite  by  its  violent  de- 
crepitation when  heated,  its  red  streak,  and  its  water  test. 

REMARKS.  —  Like  goethite  it  is  frequently  mistaken  for  and  classed  with  limonite. 
It  occurs  with  limonite  at  Salisbury,  Conn.,  and  in  various  localities  in  Prussia  and 
Siberia. 

USES.  —  It  is  an  ore  of  iron  but  commercially  is  classed  with  limonite. 

LIMONITE. — Bog-Ore,  Brown  Hematite. 

Co.  IPOSITION.  —  Fe2(OH)6Fe2O3,    (Fe,    59.8    per  cent).      Fre- 
quently quite  impure,  from  sand,  clay,  manganese,  phosphorus,  etc. 
GENERAL  DESCRIPTION.  —  Never  crystallized,  but  grading  from 

FIG.  335. 


Stalactite  of  Limonite,  Hungary.      Columbia  University. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.     275 

the  loose,  porous  bog-ore  and  earthy  ochre  of  brown  to  yellow 
color  and  dull  lustre  ;  to  compact  varieties,  often  with  smooth, 
black,  varnish-like  surface,  but  on  fracture  frequently  showing  a 
somewhat  silky  lustre  and  a  fibrous  radiated  structure.  Sometimes 
stalactitic,  Fig.  335,  and  often  with  smooth  rounded  surfaces  and 
is  pseudomorphs.  It  is  frequently  found  pseudomorphous. 

Physical  Characters.     H.,  5  to  5.5.     Sp.  gr.,  3.6  to  4. 

LUSTRE,  varnish-like,  silky,  dull.  OPAQUE. 

STREAK,  yellowish-brown,  TENACITY,  brittle,  eartny. 

COLOR,  brown,  nearly  black,  yellow  like  iron  rust. 

BEFORE  BLOWPIPE,  ETC. — In  closed  tube  yields  water,  and  be- 
comes red.  Fuses  in  thin  splinters  to  a  dark  magnetic  slag.  Usu- 
ally reacts  for  silica  and  manganese.  Soluble  in  hydrochloric 
acid,  and  may  leave  a  gelatinous  residue. 

VARIETIES. 

Bog-Iron,  loosely  aggregated  ore  from  marshy  ground,  often 
intermixed  with  and  replacing  leaves,  twigs,  etc. 

Yellow  ochre,  umber,  etc.,  earthy  material,  intermixed  with  clay. 

Brown  clay  ironstone,  compact,  often  nodular  masses,  impure 
from  clay. 

SIMILAR  SPECIES. — Distinguished  from  other  iron-ores,  except 
goethite,  by  its  streak,  and  from  the  latter  by  lack  of  crystalliza- 
tion. 

REMARKS. — The  occurrences  are  described,  p.  264.  The  largest  deposits  which 
are  regularly  mined  exist  in  the  States  of  Alabama,  Michigan  and  Tennessee. 

SIDERITE.  —  Spathic  Ore. 

COMPOSITION.  —  FeCO3,  (FeO  62.1,  CO2  37.9  per  cent.)  usually 
with  some  Ca,  Mg  or  Mn. 

GENERAL  DESCRIPTION.  —  Occurs    in  FlG  336 

granular  masses  of  a  gray  or  brown  color 
and  also  in  masses  with  rhombohedral 
cleavage  and  in  curved  rhombohedral 
crystals,  Fig.  336.  At  times  it  is  quite 
black  from  included  carbonaceous  matter. 

CRYSTALLIZATION. — Hexagonal.     Sca- 
lenohedral  class,  p.  48.   Axisr  =  0.8184. 

Usually  rhombohedrons  of  73°,  often  with  curved  (composite)  faces; 
like  those  of  dolomite. 


276 


MINERALOGY. 


Physical  Characters.     H.,  3.5  to  4.     Sp.  gr.,  3.83  to  3.88. 
LUSTRE,  vitreous  to  pearly.  OPAQUE  to  translucent. 

STREAK,  white  or  pale  yellow.  TENACITY,  brittle. 

COLOR,  gray,  yellow,  brown  or  black. 
CLEAVAGE,  rhombohedron  of  107°. 

VARIETIES  : 

Clay  Ironstone,  earthy  or  stony  mixtures,  with  silica,  clay, 
limonite,  hematite. 

Blackband,  mixtures  with  clay  and  carbon. 

Spherosiderite,  secondary  siderite  in  cavities  of  basalt  usually 
botryoidal. 

BEFORE  BLOWPIPE,  ETC. — Decrepitates,  becomes  black  and  mag- 
netic and  fuses  with  difficulty.  Soluble  in  warm  acids  with  effer- 
vescence. Slowly  soluble  in  cold  acids.  May  react  for  man- 
ganese. 

SIMILAR  SPECIES. — It  is  heavier  than  dolomite  and  becomes  mag- 
netic on  heating.  Some  stony  varieties  resemble  varieties  of  spha- 
lerite. 

REMARKS. — As  described,  p.  265,  siderite  deposits  of  economic  value  occur  as 
replacements  of  limestone  and  as  sedimentary  deposits.  Stony,  impure  "clay  iron- 
stone" and  bituminous  "black  band"  occur  as  immense  strata  in  England  and 
Wales  and  this  country  in  Pennsylvania,  Ohio,  Virginia  and  Tennessee,  always  in 
•connection  with  the  Coal  Measures.  Siderite  is  common  in  metallic  veins,  usually 
being  considered  gangue.  Sometimes,  as  at  Roxbury,  Conn.,  it  has  been  the  ore. 

USES. — It  is  used  as  an  ore  of  iron  and  when  high  in  manganese 
it  is  used  for  the  manufacture  of  spiegeleisen. 

THE  SILICATE  IRON  ORES*  (Chamosite,  Thuringite,  Greenalite,  Berthierine). 

In  various  parts  of  Europe  iron  ores  have  been  found  which  are  partly  silicates. 
Some  have  been  worked  on  an  extensive  scale.  In  this  country  the  Lake  Superior 
ores  are  believed  to  be  formed  in  considerable  part  by  the  alteration  of  such  a  silicate 
greenalite. 

COMPOSITION. — Definite  formulae  are  difficult,  chamosite,  thuringite  and  greenalite 
are  hydrous  silicates  of  iron  and  aluminum  (berthierine  is  believed  to  be  a  mixture  of 
chamosite  and  magnetite).  By  averaging  analyses  the  following  percentages  resulted. 


SiO2. 

Fe203. 

AloOa. 

FeO. 

MgO. 

H20. 

Greenalite  
Thuringite  
Chamosite  

32.86 

22.8 

26.04 

22.26 
13-5 
i-3 

17.2 
18.6 

36.40 
36.3 

39-74 

2.17 

8.48 
IO.O2 
12.41 

*  The  "green  earths,"  glauconite,  now  forming  in  the  marine  muds  and  found  in 
Cretaceous  sediments  and  celadonite  are  similar  in  composition. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     277 

GENERAL  DESCRIPTION. — Chamosite  is  usually  oolite  or  compact,  thuringite 
foliated,  greenalite  in  granules,  the  colors  range  from  gray  through  green  to  black. 

BLOWPIPE  CHARACTERS. — Chamosite  is  said  to  fuse  easily,  thuringite  less  easily, 
and  both  to  gelatinize  with  acids. 

REMARKS. — A  bed  60  ft.  thick  of  chamosite  and  thuringite  at  Schmiedefeld, 
Thuringia,  yielded  140,000  tons  in  1899.  Berthierine  at  Hayanges,  near  Metz,  is  a 
valuable  ore.  Other  deposits  exist  in  Switzerland,  France  and  Bohemia.  Greenalite 
is  abundant  in  the  Mesabi  in  the  ferruginous  cherts. 

THE   MANGANESE   MINERALS. 

The  minerals  described  are: 

Isometric 
Tetragonal 


Tetragonal 

Orthorhombic 
Hexagonal 
Triclinic 
Orthorhombic 

Other  silicates  containing  manganese  and  elsewhere  described 
are  spessartite  and  piedmontite,  and  there  are  manganiferous 
amphiboles,  pyroxenes,  axinites  and  other  species. 

Manganese  is  also  an  important  constituent  of  franklinite, 
wolframite,  huebnerite,  and  columbite. 

ECONOMIC   IMPORTANCE. 

The  principal  economic  uses  of  manganese  minerals  are  in  the 
production  of  the  alloys  with  iron,  spiegeleisen  and  ferromanganese f 
used  in  the  manufacture  of  steel,  and  in  the  making  of  manganese 
steels  to  resist  abrasion  and  shock,  such  as  car  wheels,  gears, 
crushing  machinery.  The  method  of  smelting  is  very  like  that 
used  in  the  manufacture  of  pig-iron.  Manganese  is  also  an  im- 
portant constituent  of  other  alloys,  especially  manganese  bronze 
and  so-called  silver  bronze. 

Minor  uses  are  in  the  manufacture  of  chlorine,  bromine,  oxygen, 
disinfectants,  driers  for  varnishes;  as  a  decolorizer  to  remove  the 
iron  green  color  from  glass  and  also,  when  added  in  larger  quantity, 
to  give  an  amethystine  color  to  glass  and  pottery;  in  the  ordinary 


Sulphide 

Alabandite 

MnS 

Oxides 

Braunite 

Mn2O3 

Hausmannite 

Mn3O4 

Pyrolusite 

MnO2 

Polianite 

MnO2 

Psilomelane 

MnO2  +  (H2O. 

,K2O.BaO) 

Wad 

Mixture  of  oxides 

Hydroxide 

Manganite 

MnO(OH) 

Carbonate 

Rhodochrosite 

MnC03 

Silicates 

Rhodonite 

MnSiOs 

Tephroite 

Mn2SiO4 

278  MINERALOGY. 

dry  battery;   in  calico  printing,  making  green  and  violet  paints, 
etc. 

Certain  iron  ores  are  very  rich  in  manganese  and  are  valuable  in 
making  spiegeleisen.  In  1914,*  445,827  long  tons  of  mangan- 
iferous  iron  ores  were  mined  in  the  United  States.  Also  a  large 
amount  of  franklinite  was  used  for  the  production  of  zinc  oxide  and 
100,198  tons*  of  a  highly  manganiferous  by-product  obtained. 

In  the  West,  especially  in  Colorado  and  Arizona,  manganese 
ores  often  carry  silver,  and  several  thousand  tons  are  smelted  each 
year  with  other  silver-bearing  minerals,  the  manganese  acting  as  a 
flux.  Much  of  the  Arkansas  material  is  also  used  as  flux.  In 
1914,  39,881  tons  were  thus  used. 

The  manganese  minerals  important  as  ores  are  the  oxides 
pyrolusite,  psilomelane  (including  wad),  braunite  and  manganite, 
and  sometimes  rhodochrosite.  In  1914!  2,635  tons  were  produced 
mainly  in  Virginia,  Arkansas  and  Georgia. 

Owing  chiefly  to  the  fact  that  "most  of  the  known  manganese 
ore  deposits  of  the  United  States  yield  material  that  must  be  washed 
or  concentrated  to  obtain  a  marketable  product"*  this  country 
imports  most  of  its  material  from  Russia,  India  and  Brazil.  In 
1914  the  comparison  in  long  tons  was: 

Production.  Imports. 

Manganese  Ore 2,635  283,294 

Ferromanganese 100,731  82,997 

Spiegeleisen 76,625  2,870 

THE   FORMATION   AND    OCCURRENCE   OF   MANGANESE   ORES. 

The  Primary  Sources. 

The  igneous  rocks  contain  a  small  percentage  of  manganese 
(Mn  0.77  per  cent.,  Clarke),  syenites,  porphyries,  and  basalts  are 
said  to  contain  about  0.36  per  cent.  (Lindgren). 

The  schists  also  contain  small  percentages  of  manganese  and 
certain^  schists  carry  manganese  silicates,  rhodonite  and  tephroite 
or  one  or  more  of  spessartite  (manganese  garnet),  piedmontite 
(manganese  epidote).  or  manganese  varieties  of  pyroxene  or  amphi- 
bole. 

*  Mineral  Resources  of  Ihe  U.  S.,  1914, 

t  D.  F.  Hewett  in  Mineral  Resources  of  the  U.  S.,  1914,  Ft.  i,  p.  166. 

t  See  under  residual  deposits,  next  page. 


MINERALS  .  OF  METALLIFEROUS    ORE   DEPOSITS.     279 

The  sedimentary  rocks  contain  manganese  as  oxides  or  rhodonite 
or  rhodochrosite. 

The  ores  are  secondary  and  are  the  result  usually  of  weathering 
and  concentration  in  some  instances  combined  with  contact  action. 
The  resulting  deposits  are  chiefly  oxides  and  sometimes  carbonates 
and  classify  as : 

Contact  Deposits — containing  hausmannite,  braunite,  franklinite, 
rhodonite,  tephroite,  etc.,  as  at  Langban  and  other  Wermland 
deposits  of  Sweden  and  at  Franklin  Furnace,  N.  J. 

Veins  (lateral  secretions)  containing  pyrolusite,  psilomelane, 
manganite,  poliantite,  as  at  Schwarzenberg,  Saxony;  Ihlefeld, 
Harz;  and  Thuringer  Wald;  and  at  Veitsch,  Styria;  chiefly  rho- 
dochrosite. 

Replacements,  consisting  of  rhodochrosite  or  the  oxides,  lime- 
stones by  rhodochrosite,  Las  Cabesses,  French  Pyrenees;  porphyry 
with  exception  of  quartz  by  oxides,  Thuringer  Wald. 

Sedimentaryf  deposits. 

Consisting  of  pyrolusite,  psilomelane,  manganite  and  earthy 
mixtures  called  wad. 

As  Bog  Ores,  usually  with  bog  iron  and  often  by  aid  of  organisms. 
Wickes,  Mont.;  Hillsborough,  New  Brunswick;  Norway,  Sweden. 

^4 s  Lake  or  Sea  Beds.  The  enormous  deposit  of  Kutais,  Trans- 
Caucasus  are  oolitic  pyrolusite  cemented  by  earthy  manganese. 

Residual  Deposits,  chiefly  pyrolusits,  psilomelane  and  wad, 
sometimes  braunite.  India  from  decomposing  archaean  rocks 
carrying  spessartite  and  rhodonite.  Often  with  enormous  masses 
of  psilomelane,  pyrolusite  or  braunite.  Brazil  (Minas  Geraes)  from 
decomposing  schists  carrying  rhodonite,  tephroite  and  spessartite. 
Texas  from  decomposing  schists  carrying  spessartite,  piedmontite 
and  tephroite.  Cremora,  Va. — in  concentric  layers  of  pyrolusite 
and  psilomelane  forming  lumps  and  larger  bodies  in  clay. 

*  "The  lode-like  manganese  deposits  on  the  north  side  of  the  Thuringer  Wald 
exhibit  a  transformation  so  complete  that  only  the  quartz  of  the  original  rock  remains 
unaffected."  Beyschlag,  Vogt  and  Krusch,  Truscott,  142. 

t  They  are  frequently  near  similar  deposits  of  iron  but  on  account  of  the  relatively 
easier  solubility  of  the  manganese  carbonate  the  deposits  usually  separate.  The 
manganese  oxides  are  probably  precipitated  in  the  colloidal  condition,  with  a  tendency 
to  absorb  certain  oxides  especially  of  barium  and  potassium  but  in  time  crystallize. 


280  MINERALOGY. 

MANGANIFEROUS   IRON   OR   SILVER   OR   ZINC   ORES. 

By  far  the  larger  portion  of  the  manganese  mined  in  the  United 
States  is  in  the  form  of  mixtures  of  iron  oxides,  with  relatively 
small  proportions  of  manganese  oxides,  these  are  obtained  chiefly 
from  the  Lake  Superior  region  and  also  from  Colorado  and 
Arkansas. 

Manganese  residues  are  obtained  from  the  zinc  ores  of  Franklin 
Furnace,  N.  J. 

Manganiferous  silver  ores  consisting  of  psilomelane  and  probably 
other  oxides  with  small  quantities  of  silver  and  lead  minerals  are 
found  near  the  ore  bodies  at  Leadville  and  elsewhere  and  used  as 
fluxes,  silver  being  recovered. 

ALABANDITE.— Manganblende. 

COMPOSITION. — MnS,  (Mn  63.1,  S  36.9  per  cent.). 

GENERAL  DESCRIPTION. — A  dark  iron-black  metallic  mineral  with  an  olive  green 
streak.  Usually  massive,  with  easy  cubic  cleavage  and  occasionally  in  cubic  or  other 
isometric  crystals.  Also  massive  granular 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color,  deep  black  with  brown 
tarnish.  Streak,  olive  green.  H.,  3.5  to  4.  Sp.  gr.,  3.95  to  4.04.  Brittle. 

BEFORE  BLOWPIPE,  ETC. — Turns  brown,  evolves  sulphur  dioxide  and  fuses. 
Gives  sulphur  reactions  with  soda.  Soluble  in  dilute  hydrochloric  acid  with  rapid 
evolution  of  hydrogen  sulphide. 

SIMILAR  SPECIES It  is  distinguished  from  all  similar  species  by  its  streak. 

REMARKS.— The  other  manganese  minerals  are  derived  in  part  from  the  alteration 
of  this  species.  It  occurs  with  other  metallic  sulphides. 

BRAUNITE. 

COMPOSITION. — Mn2O3,  but  usually  containing  MnSiO3. 
GENERAL  DESCRIPTION. — Brownish  black  granular  masses  and 
occasional  minute  tetragonal  pyramids  almost  isometric,  t  —  0.985. 

Physical  Characters.     H,,  6  to  6.5.     Sp.  gr.,  4.75  to  4.82. 
LUSTRE,  submetallic.  OPAQUE. 

STREAK,  brownish  black.  TENACITY,  brittle. 

COLOR,  brownish  black  to  steel  gray. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  With  borax  an  amethys- 
tine bead.  Soluble  in  hydrochloric  acid,  evolving  chlorine  and 
generally  leaving  gelatinous  silica. 

SIMILAR  SPECIES. — Resembles  hausmannite,  but  has  a  darker 
streak  and  is  harder. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.      281 
FIG.  337.  FIG.  338.  FIG.  339. 


Braunite,  pp  =  70°  7'. 


Hausmannite,  pp  =  74°  34'. 


REMARKS. — As  stated  on  p.  279,  it  occurs  as  important  ore  in  the  contact  deposits 
of  Langban,  etc.,  Sweden,  and  as  large  masses  in  the  residual  deposits  of  Vizianagram, 
India.  In  the  veins  at  Ilmenau,  Thuringia,  and  Ihlfeld  Hartz  it  occurs  crystallized 
and  massive,  and  it  forms  part  of  the  Batesville,  Arkansas,  residual  deposit. 

HAUSMANNITE. 

COMPOSITION. — MngO^.     (Mri,Os  69.0,  MnO  31.0  per  cent.). 

GENERAL  DESCRIPTION. — Black  granular  strongly  coherent  masses  occasionally  in 
simple  and  twinned  tetragonal  pyramids  which  are  more  acute  than  those  of  braunite, 
c=  1-174. 

PHYSICAL  CHARACTERS.— -Opaque.  Lustre,  submetallic.  Color,  brownish  black. 
Streak,  chestnut  brown.  H.,  5  to  5.5.  Sp.  gr.,  4.72  to  4.85.  Strongly  coherent. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  Colors  borax  bead  amethystine.  Soluble 
in  hydrochloric  acid  with  evolution  of  chlorine. 

SIMILAR  SPECIES. — Differs  from  braunite  in  hardness,  streak  and  absence  of  silica. 

PYROLUSITE.— Black  Oxide  of  Manganese. 

COMPOSITION. — MnO2,    (Mn  63.2  per  cent.). 

GENERAL  DESCRIPTION. — A  soft  black  mineral  of  metallic  lustre. 
Frequently  composed  of  short  indistinct  crystals  or  radiated  needles, 
but  also  found  compact,  massive,  stalactitic,  and  as  velvety  crusts. 
Usually  soils  the  fingers.  Frequently  in  alternate  layers  with 
psilomelane. 


Physical  Characters.    H.,  i  to  2.5. 
LUSTRE,  metallic  or  dull. 
STREAK,  black. 
COLOR,  black  to  steel  gray. 


Sp.  gr.,  4.7  to  4.86. 

OPAQUE. 

TENACITY,  rather  brittle. 


BEFORE  BLOWPIPE,  ETC. — Infusible,  becomes  brown.  Usually 
yields  oxygen  and  a  little  water  in  closed  tube.  Colors  borax 
bead  amethystine.  Soluble  in  hydrochloric  acid  with  evolution  of 
chlorine. 


282  -        MINERALOGY, 

SIMILAR  Species. — Distinguished  by  its  softness  and  black  streak 
from  other  manganese  minerals. 

REMARKS. — As  described  on  p.  279,  occurs  in  the  vein,  replacement,  sedimentary 
and  residual  deposits  and  usually  associated  with  psilomelane. 

The  great  sedimentary  deposit  at  Kutais,  Transcaucasia,  is  compact  pyrolusite 
separated  by  mixed  ores  and  has  a  thickness  of  six  to  sixteen  feet.  Another  enormous 
deposit  exists  at  Nicopol. 

In  this  country  the  residual  deposits  at  Crimera,  Va.,  Carters ville,  Ga.,  and 
Batesville,  Ark.,  and  the  streaks  and  pockets  in  certain  hematites  of  Lake  Superior 
are  the  important  deposits.  Other  deposits  exist  in  California,  Vermont  and  North 
Carolina.  The  purest  material  for  use  in  glass  making  is  obtained  near  Sussex,  N.  B.f 
and  from  the  Tenny  Cape  district,  Nova  Scotia. 

POLIANITE. 

COMPOSITION. — MnC>2  (Mn  63.1  per  cent.). 

GENERAL  DESCRIPTION. — A  hard,  dark  gray,  submetallic  substance  occurring  in 
composite  groups  of  minute  crystals  or  as  an  outer  coating  on  manganite. 

CRYSTALLIZATION. — Tetragonal  c  =  .6646.  Small  crystals  on  pyrolusite  or 
parallel  groupings  of  pseudorhombic  shape. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  submetallic.  Color,  steel  to  iron 
gray.  Streak,  black.  H.,  6  -6.5.  Sp.  gr.,  4.83-5.02. 

BEFORE  BLOWPIPE,  ETC. — Like  pyrolusite. 

REMARKS. — Occurs  at  Flatten,  Bohemia,  in  the  typical  crystal  groups.  In  other 
localities  is  often  entirely  or  partly  changed  to  pyrolusite. 

MANGANITE. 

COMPOSITION.— MnO(OH),  (Mn  62.4,0  27.3,  H2O  10.3  per  cent). 
GENERAL  DESCRIPTION. — Occurs  in  long  and  short  prismatic 

FIG.  340. 


Manganite,  Ilefeld,  Hartz.     N.  Y.  State  Museum. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.      283 

(orthorhombic)  crystals  often  grouped  in  bundles  with  fluted  or 
rounded  cross-section  and  undulating  terminal  surface,  rarely  mass- 
ive,  granular  or  stalactitic. 

Physical  Characters,     H.,  4.     Sp.  gr.,  4.2  to  4.4. 

LUSTRE,  submetallic.  OPAQUE. 

STREAK,  reddish  brown  to  black.  TENACITY,  brittle. 

COLOR,  steel  gray  to  iron  black. 

BEFORE  BLOWPIPE,  ETC. — Like  pyrolusite,  but  yields  decidedtesk 
for  water  and  very  little  oxygen. 

REMARKS. — Formed  in  the  same  deposits  as  pyrolusite  and  frequently  altered  to 
pyrolusite. 

PSILOMELANE.— Black  Hematite. 

COMPOSITION.— Perhaps  MnO2+  (H2O,  K2O  or  BaO)  or  H4MnO6, 
with  replacement  by  Ba  or  K. 

GENERAL  DESCRIPTION. — A  smooth  black  massive  mineral  com- 
monly botryoidal,  stalactitic  or  in  layers  with  pyrolusite.  Never 
crystallized. 

Physical  Characters.     H.,  5  to  6.  Sp.  gr.,  3.7  to  4.7. 
LUSTRE,  submetallic  or  dull.  OPAQUE. 

STREAK,  brownish  black.  TENACITY,  brittle. 

COLOR,  iron  black  to  dark  gray. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  In  closed  tube  yields 
oxygen  and  usually  water.  Soluble  in  hydrochloric  acid,  with 
evolution  of  chlorine.  A  drop  of  sulphuric  acid  added  to  the  solu- 
tion will  usually  produce  a  white  precipitate  of  barium  sulphate. 

SIMILAR  SPECIES. — Distinguished  from  pyrolusite  by  its  hard- 
ness, and  from  limonite  by  its  streak. 

REMARKS. — Its  localities  are  the  same  as  for  pyrolusite,  and  the  two  minerals  are 
usually  mined  together. 

WAD. — Bog  Manganese. 

COMPOSITION. — Mixture  of  manganese  oxides,  with  often  oxides  of  metals  other 
than  manganese  such  as  cobalt,  copper  and  lead. 

GENERAL   DESCRIPTION. — Earthy   to   compact   indefinite   mixtures  of  different 
metallic  oxides,  in  which  those  of  manganese  predominate.     Dark  brown  or  black  ' 
in  color;  often  soft  and  loose,  but  sometimes  hard  and  compact. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre  dull.  Color  brown  to  black.  Streak 
brown.  H.,  1/2  to  6.  Sp.  gr.,  3  to  4.26.  Often  soils  the  fingers. 

BEFORE  BLOWPIPE,  ETC. — As  for  psilomelane,  but  often  with  strong  cobalt  or 
copper  reactions. 


284  MINERALOGY. 

USES. — Wad  is  used  as  a  paint  and  in  the  manufacture  of  chlorine. 
REMARKS. — Large  deposits  exist  at  Wickes,  Montana;  Hillsborough,  New  Bruns- 
wick; and  Norway. 

RHODOCHROSITE. 

COMPOSITION.  —  MnCO3,  (MnO  61.7,  CO2  38.3  per  cent.)  with 
partial  replacement  by  Ca,  Mg  or  Fe. 

GENERAL  DESCRIPTION. — Rose  pink  to  brownish  red  rhombo- 
hedral  crystals,  usually  small  and  curved  like  dolomite.  Fre- 
quently massive  cleavable,  or  granular  or  compact.  Less  fre- 
quently botryoidal  or  incrusting. 

CRYSTALLIZATION.  —  Hexagonal.    Scalen-  FIG.  341. 

ohedral  class,  p.  48.  Axis  ^=.8184.  An- 
gles as  in  siderite.  Usual  form  a  rhombo- 
hedron  of  7  3  ° .  Optically  — . 


Physical  Characters.     H . ,  3 . 5  to  4. 5 . 
gr.,  3.3  to  3.6. 

LUSTRE,  vitreous  to  pearly.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  light  pink,  rose  red,  brownish  red  and  brown. 

CLEAVAGE,  parallel  to  rhombohedron. 

BEFORE  BLOWPIPE,  ETC.  —  Infusible,  but  decrepitates  violently 
and  becomes  dark  colored.*  In  borax  yields  amethystine  bead. 
Soluble  in  warm  hydrochloric  acid,  with  effervescence,  slowly  sol- 
uble in  the  cold  acid. 

SIMILAR  SPECIES.  —  Distinguished  from  rhodonite  by  form, 
cleavage,  effervescence  and  infusibility. 

REMARKS. — The  great  manganese  deposits  of  Huelva,  Spain,  are  chiefly  rhodo- 
chrosite,  containing  rhodonite,  and  this  is  being  mined  in  enormous  quantities. 
In  the  Quelez  District,  Brazil,  rhodochrosite  with  tephroite  forms  large  lenses  which 
by  alteration  have  yielded  psilomelane.  Other  producing  localities  are  Merioneth- 
shire, Wales,  and  Chevron,  Belgium.  It  is  also  found  in  ore-veins,  as  a  gangue 
mineral  in  the  silver  veins  of  Butte,  Montana,  Austin,  Nev.,  and  elsewhere.  It  is 
not  mined,  in  this  country. 

RHODONITE. 

COMPOSITION.  —  MnSiO3,  with  replacement  by  Fe,  Zn  or  Ca. 
GENERAL    DESCRIPTION.  —  Brownish    red    to    bright    red,    fine 

*  May  become  magnetic  from  impurities. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.      285 

grained    or  cleavable  masses  and  dissemi-  FIG.  342. 

nated    grains,   often    coated    with    a   black 

oxide.    Sometimes  in  triclinic  crystals  either 

tabular  parallel  to  c  or  like  the  forms  of 

pyroxene. 

CRYSTALLIZATION. — Fig.  342  shows  three 
pinacoids  a,  b  and  cy  the  hemi-unit  prisms 
m  and  Mt  and  two  quarter  pyramids  vt  and 
tv  of  &  :  b  :  2c.  The  supplement  angles  are  Franklin  Furnace. 

mM=  92°  28' ;  cm=*  68°  45'  ;  cM=  86°  23'. 

Physical  Characters.  H.,5.$  to  6.5.  Sp.  Gr.,  3.4  to  3.68. 

LUSTRE,  vitreous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  brownish-red  to  flesh-red,  bright-red,  greenish, yellowish. 

BEFORE  BLOWPIPE,  ETC. — Blackens  and  fuses  easily  with  slight 
intumescence.  With  fluxes  reacts  for  manganese  and  zinc.  In 
powder  is  partially  dissolved  by  hydrochloric  acid,  leaving  a  white 
residue.  If  altered  may  effervesce  slightly  during  solution. 

REMARKS. — In  the  gneisses  and  crystalline  schists  rhodonite  occurs  as  a  primary 
alteration  product  as  interbedded  layers,  lenses  and  beds  often  of  considerable 
extent  as  near  Ekaterinenberg,  Urals,  Langban,  Sweden  (with  iron  ore  beds) 
Bukowina,  Russia.  Near  Rosenau,  Hungary,  the  deposit  is  over  forty  feet  thick. 
Many  other  localities  exist. 

In  the  United  States  it  occurs  at  Blue  Hill,  Maine,  Cummington,  Mass.,  Franklin, 
N.  J.,  in  the  ore  veins  of  Butte,  Montana,  and  elsewhere. 

USES. — Probably  to  some  extent  as  an  ore  and  a  small  amount 
is  polished  as  an  ornamental  stone.  Chiefly  important  as  a  source 
of  the  oxides. 

TEPHROITE. 

COMPOSITION. — Mn2SiO4  (MnO.7o.2,  SiO2  29.8  per  cent.).  Usually  with  some 
MgO,  sometimes  with  ZnO. 

GENERAL  DESCRIPTION. — As  gray  to  flesh  red  masses  which  cleave  (?)  in  direc- 
tions at  right  angles. 

CRYSTALLIZATION. — Orthorhombic;  crystals  rare,  a  :  ~b  :  I  =  .4621  :  i  :  .5914. 

PHYSICAL  CHARACTERS. — Translucent  to  transparent.  Lustre,  vitreous  to  greasy. 
Color,  ash  gray,  flesh  red,  brown.  Streak,  gray.  H.,  5.5  to  6.  Sp.  gr.,  4  to  4.1. 

BEFORE  BLOWPIPE,  ETC. — Fusible  with  some  difficulty.  Soluble  in  hydrochloric 
acid  with  gelatinous  residue. 

REMARKS. — Common  in  certain  rocks  which  by  their  alteration  have  yielded 
manganese  deposits  as  in  central  Texas  and  in  the  Lafayette  District,  Brazil.  First 
discovered  among  the  Franklin  Furnace  minerals  and  later  in  the  Langban  and 
Paisberg,  Sweden,  deposits  in  small  crystals. 


Millerite 

NiS 

Hexagonal 

Pentlandite 

(Fe.Ni)S 

Isometric 

Niccolite 

NiAs 

Hexagonal 

Annabergite 

Ni3(AsO4)2.8H2O 

Monoclinic 

Garnierite 

H2(Ni.Mg)SiO4.H2O 

MINERAL  OGY. 


THE    NICKEL  AND    COBALT   MINERALS. 

The  cobalt  minerals  described  are: 

Sulphide  Linnaeite  (Co.Ni)sS4  Isometric 

Sulpharsenide  Cobaltite  CoAsS  Isometric 

Arsenide  Smaltite  (Co.Ni)As2  Isometric 

Arsenate  Erythrite  Co3(AsO4)2.8H2O  Monoclinic 

Cobaltiferous  arsenopyrite,  pyrite  and  pyrrhotite  occur. 
The  nickel  minerals  described  are  : 

Sulphides 

Arsenide 
Arsenate 
Silicates 

Chloanthite,  or  highly  nickeliferous  smaltite;  and  nickeliferous 
pyrrhotite  and  pyrite  in  which  the  nickel  is  supposed  to  be  present 
as  pentlandite  are  important  ores. 

ECONOMIC   IMPORTANCE. 

Cobalt. 

The  metal  cobalt  has,  as  yet,  no  important  use  ;  the  oxide  is 
used  to  impart  a  blue  color  to  glass  and  pottery.  The  chief  com- 
mercial compound  is  SMALT,  a  cobalt  glass,  the  cobalt  replacing 
the  calcium  of  ordinary  glass.  This  is  ground  and  used  as  a  fine 
blue  pigment,  which  is  unaltered  by  exposure. 

Cobalt  blue  and  Rinmann's  green  are  compounds  of  cobalt  with 
alumina  and  zinc  oxide  respectively. 

The  extraction  of  cobalt  from  a  nickeliferous  matte  is  an  elabor- 
ate chemical  operation  involving-  solution  in  hydrochloric  acid,  pre- 
cipitation of  manganese  and  iron  as  basic  carbonates,  and  of  other 
metals  as  sulphides,  leaving  a  solution  of  chloride  of  nickel  and 
cobalt.  From  these  the  cobalt  is  precipitated  with  great  care,  by 
means  of  calcium  hypochlorite,  as  cobaltic  hydroxide,  after  which 
the  nickel  is  precipitated  as  hydroxide  by  lime-water.  By  using 
selected  ores,  mattes  especially  rich  in  cobalt  may  be  obtained  and 
for  ordinary  purposes  the  small  nickel  contents  are  neglected. 

The  amount  of  available  cobalt  ore  has  been  greatly  increased 
of  late  due  to  the  silver-bearing  cobalt  ores  of  Cobalt,  Ont.,  but 
the  amount  used  is  small,  approximating  20  tons  of  the  oxide 
each  year  in  this  country. 


MINERALS   OF  METALLIFEROUS    ORE  DEPOSITS.      287 

No  production  of  cobalt  ores  is  reported  for  1914*  in  this 
country,  but  Ontario  produced  97  tons  of  ore  and  New  Caledonia 
exported  920  tons  of  ore  and  25  tons  of  matte.  Germany  elec- 
trolytically  separates  cobalt  from  copper  of  Belgian  Congo. 

Metallic  nickel  is  extensively  used  in  different  alloys,  and,  in- 
deed, was  first  obtained  as  a  residual  alloy  with  copper,  iron  and 
arsenic,  in  the  manufacture  of  smalt.  This  alloy  was  called  Ger- 
man silver  or  nickel  silver  and  largely  used  in  plated  silverware. 
Later,  a  large  use  for  nickel  was  found  in  coins,  the  United  States 
Mint  alone  using  nearly  one  million  pounds  between  1857  and 
1884.  In  this  alloy  copper  is  in  large  proportion,  the  present 
five  cent  piece  being  25  per  cent,  nickel,  75  per  cent,  copper,  and 
in  other  coins  the  percentage  of  copper  being  still  greater.  The 
most  extensive  application  of  nickel  at  present  is  in  the  manufac- 
ture of  nickel  steel  for  armor  plates  and  other  purposes.  The 
uses  of  nickel  steel  are  continually  increasing,  as  the  metal  has 
some  excellent  properties  possessed  by  no  other  alloy.  To  a 
limited  extent  nickel  is  used  in  a  nickel-copper  alloy  for  casing 
rifle  bullets.  An  alloy  of  iron  and  nickel  containing  30  per  cent, 
of  nickel  is  non-magnetic  and  is  used  in  electric  heaters  and  in  parts 
of  other  electrical  apparatus. 

"Monel  metal"  an  alloy  of  68  per  cent,  nickel,  1.5  per  cent,  iron 
and  30.5  per  cent,  copper  made  by  extracting  the  nickel  and  copper 
from  the  ore  without  separating  them,  is  said  to  be  stronger  than 
nickel  steel,  unaffected  by  sulphuric  acid  and  silver  white  in  color. 

A  sulphate  of  nickel  and  ammonium  is  also  manufactured  in 
large  amounts  for  use  in  nickel  plating. 

The  nickel  of  commerce  is  nearly  all  obtained  either  from  the 
garnierite  of  New  Caledonia  or  from  the  deposit  of  nickel-bear- 
ing sulphides  of  Ontario.  The  garnierite  is  smelted  in  a  low  blast 
furnace,  with  coke  and  gypsum,  and  the  matte  of  nickel,  iron  and 
sulphur  thus  produced  is  alternately  roasted  and  fused  with  sand, 
in  a  reverberatory  furnace,  until  nearly  all  the  iron  has  been  re- 
moved. The  nickel  sulphide,  by  oxidation,  is  converted  into  oxide. 

Nickel  oxide  is  obtained  from 'the  pyrrhotite  and  chalcopyrite 
of  Sudbury,  Canada.  The  ore  is  first  roasted  to  remove  much 
of  the  sulphur,  and  is  then  smelted,  together  with  nickel-bear- 
ing slags  of  previous  operations.  A  nickel  matte  carrying  much 

*  Mineral  Industry,  1914,  p.  548. 


288  MINERALOGY. 

copper  and  some  iron  is  produced  through  which  air  is  blown 
in  a  silica -lined  Bessemer  converter  and  most  of  the  iron  is 
carried  into  the  slag.  A  matte,  rich  in  nickel  and  copper,  results. 
This  may  be  directly  roasted  and  reduced  by  carbon  to  produce 
nickel-copper  alloys  for  the  manufacture  of  German  silver.  In 
order  to  separate  the  nickel  the  concentrated  matte  is  fused  with 
sodium  sulphate  and  coke,  after  which  the  melted  sulphides  are 
allowed  to  settle.  Under  these  conditions  the  copper  and  iron 
sulphides  form  a  very  fluid  mass  with  the  soda,  and,  with  some 
nickel,  rise  to  the  top  while  the  lower  portions  of  the  mass  are 
highly  nickeliferous.  The  two  layers  are  separated  and  each  is 
re-treated  in  much  the  same  manner.  The  nickel  sulphide  result- 
ing is  partially  roasted  and  is  fused  with  sand,  by  means  of  which 
most  of  the  iron  is  removed  as  a  silicate  in  the  slag.  The  nickel 
sulphide  remaining  is  by  oxidation  converted  into  the  oxide.  The 
oxide  is  sold  directly  to  steel  makers  or  may  be  reduced  to  metal 
by  mixing  with  charcoal  and  heating,  white  hot,  in  a  graphite 
crucible. 

No  nickel  ore  is  reported  as  produced  in  this  country  in  1914. 
Canada  produced*  ore  containing  12,937  short  tons  of  nickel  in 
addition  to  about  200  tons  of  nickel  oxide.  New  Caledonia 
exported  94,154  tons  of  ore  and  5,287  tons  of  matte.  Norway 
and  Germany  were  also  producers. 

Nickel  is  now  successfully  refined  by  electrolysis,  but  the  de- 
tails of  the  process  are  jealously  guarded.  It  is  doubtful,  however, 
if  nickel  can  be  separated  from  cobalt  in  this  manner,  although 
most  other  impurities  are  removed. 

The  Mond  process  for  the  extraction  of  nickel  from  its  ore  and 
for  its  separation  from  cobalt  promises  to  become  important.  The 
process  is  based  on  the  discovery  that  when  carbon  monoxide 
is  passed  over  heated  nickel,  volatile  nickel  carbonyl,  Ni(CO)4 
is  formed.  As  cobalt  does  not  react  in  this  way,  the  separation 
of  nickel  from  cobalt  is  easily  accomplished.  The  reconversion  of 
the  nickel  carbonyl  into  nickel  and  carbon  monoxide  is  a  simple 
operation. 

THE  FORMATION  AND  OCCURRENCE  OF  COBALT  AND  NICKEL  ORES 
Nickel  and  cobalt  occur  usually  together  and  are  present  in 

*  Mineral  Industry,  1914. 


MINERALS   OF  METALLIFEROUS    ORE  DEPOSITS.      289 


the   earth's   crust  in   minute  percentages.     Nickel  less  than  .01 
(Clarke),  cobalt  between  .001  and  .0001  (Vogt). 

The  peridotites  and  pyroxenic  rocks  and  the  serpentines  derived  from  them 
contain  most  of  these  elements. 

The  occurrences  of  importance  are  principally: 

Magmatic  Segregations. 

(a)  Of  nickeliferous  pyrrhotite  and  pyrite  and  various  nickel  and 
cobalt  minerals,  especially  pentlandite  or  millerite,  as  at  Sudbury, 
Ontario;  Gap  Mine,  Pennsylvania;  and  many  small  deposits  in 
Norway,  (b)  Of  iron  nickel  alloys  see  Iron,  p.  266. 

Normal  Veins. 

Containing  sulphides  and  arsenides  (smaltite,  chloanthite,  nic- 
colite,  linnceite,  cobaltite  and  rarer  species).  In  schists  and  gneiss 
and  conglomerates  near  basic  intrusive  dikes  and  in  the  dikes 
themselves,  as  at  the  Cobalt,  Ontario,  district  and  Annaberg 
and  Schneeberg,  Saxony;  and  Dobschau,  Hungary. 

Veins  in  Serpentine  (Lateral  Secretion)  containing  hydrous 
silicates  or  oxides,  garnierite,  genthite,  pimelite  or  asbolane.  Due 
to  a  weathering  of  the  peridotite  to  serpentine  with  a  concentra- 
tion of  the  nickel  or  cobalt  in  the  cracks  and  fissures  as  in  the 
garnierite  and  asbolane  deposits  of  New  Caledonia  and  the  pimelite 
of  Frankenstein,  Silesia. 

LINN^ITE.  — Cobalt  Pyrites. 

COMPOSITION. — (Co.Ni)3S4,  often  with  some  Fe  or  Cu  replacing. 

GENERAL  DESCRIPTION.  —  A  steel-gray  metallic  mineral  usually 
in  granular  or  compact  masses  intermixed  frequently  with  chal- 
copyrite ;  also  in  small  isometric  crystals,  usually  the  octahedron 
p,  Fig.  343,  or  this  with  the  cube  a,  Fig.  344. 


FIG.  343. 


FIG.  344. 


20 


290 


MINERALOGY. 


Physical  Characters.     H.,  5.5.     Sp.  gr.,  4.8  to  5. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  nearly  black.  TENACITY,  brittle. 

COLOR,  steel-gray,  with  reddish-tarnish. 
CLEAVAGE,  cubic  imperfect. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  to  a  magnetic  glob- 
ule, and  gives  off  fumes  of  sulphur  dioxide.  In  borax  bead  gives  a 
deep  blue  color,  and  with  frequent  replacement  of  borax  the  red 
bead  of  nickel  may  be  obtained.  Soluble  in  nitric  acid  to  a  red 
solution  and  with  separation  of  sulphur. 

REMARKS. — Occurs  in  veins  at  Miisen  and  Siegen,  Prussia,  and  Mineral  Hill, 
Maryland.  It  occurs  mostly  massive  with  other  cobalt  and  nickel  minerals  and  with 
chalcopyrite,  pyrrhotite,  bornite,  at  Mine  La  Motte,  Mo.,  Lovelock's  Station,  Nev., 
and  in  a  few  other  American  localities. 

USES. — Does  not  occur  in  large  amounts,  but  is  used  as  a  source 
of  both  cobalt  and  nickel. 

COBALTITE.— Cobalt  Glance. 

COMPOSITION. — CoAsS,     (Co  35.5,  As  45.2,  S  19.3  per  cent.) 

GENERAL  DESCRIPTION. — A  silver  white  to  gray  metallic  min- 
eral resembling  linnaeite  in  massive  state  but  in  crystals  differing  in 
that  the  forms  are  the  pyritohedron  e,  and  cube  #,  and  these  com- 
bined, Fig.  347. 
Physical  Characters.     H.,  5.5.     Sp.  gr.,  6  to  6.1. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  black.  TENACITY,  brittle. 

COLOR,  silver  white  to  gray.  CLEAVAGE,  cubic. 

BEFORE  BLOWPIPE,  ETC.  —  On  charcoal  fuses  to  a  magnetic 
globule  and  evolves  white  fumes  with  garlic  odor.  Unaltered  in 
closed  tube.  Soluble  in  warm  nitric  acid  to  rose-red  solution,  with 
residue  of  sulphur  and  arsenous  oxide. 

FIG   345.  FIG.  346.  FIG.  347. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.     291 

REMARKS. — Cobaltite  occurs  in  large  quantities  as  an  independent  stratum  2  feet 
thick,  near  Daschkessan,  Caucasus,  underlying  magnetite.  At  Skutterud,  Norway, 
it  occurs  free  from  nickel  massive  and  disseminated  in  mica  schist.  In  Saxony  in 
veins  with  barite.  At  the  Cobalt  region,  Ontario,  and  in  Grant  Co.,  Oregon,  in 
small  amounts. 

SMALTITE.— CHLOANTHITE.* 

COMPOSITION.  —  (Co.Ni)As2,  varying  widely  in  proportion  of 
cobalt  and  nickel,  and  usually  containing  some  iron  also. 

GENERAL  DESCRIPTION. — A  tin-white  to  steel-gray  metallic  min- 
eral resembling  linnaeite  and  cobaltite.  Usually  occurs  granular 
massive,  but  also  in  isometric  crystals,  especially  modified  cubes 
with  curved  faces. 

Physical  Characters.     H.,  5.5  to  6.  Sp.  gr.,  6.4  to  6.6. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  black.  TENACITY,  brittle. 

COLOR,  tin-white  to  steel-gray.  CLEAVAGE,  octahedral. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses,  yields  white  fumes 
with  garlic  odor  and  leaves  a  magnetic  residue,  which,  when  oxi- 
dized in  contact  with  frequently  replaced  borax,  yields  successively 
slags  colored  by  iron,  cobalt,  nickel  and  possibly  by  copper.  In 
closed  tube  yields  arsenical  mirror.  (If  sulphur  is  present  also 
yields  a  red  sublimate.) 

Soluble  in  nitric  acid  to  a  red  to  green  solution  according  to 
proportion  of  cobalt  and  nickel.  Partially  soluble  in  hydrochloric 
acid,  especially  so  after  fusion,  but  yields  no  voluminous  precipitate 
of  yellow  arsenic  sulphide,  as  does  arsenopyrite  when  similarly 
treated. 

SIMILAR  SPECIES. — Differs  from  linnaeite  and  cobaltite  in  cleav- 
age, specific  gravity  and  blowpipe  reactions.  Differs  from  most 
arsenopyrite  and  tetrahedrite  in  the  cobalt  blue  slags  which  it 
yields.  It  can  best  be  distinguished  from  cobaltiferous  arseno- 
pyrite by  the  reaction  in  acids  after  fusion. 

REMARKS. — Occurs  in  veins  as  stated  on  p.  289.  It  was  the  original  mineral 
deposited  in  the  veins  at  the  Cobalt  district,  Ontario.  It  occurs  also  in  veins  at 
Annaberg  and  Schneeberg,  Saxony,  Reichelsdorf,  Hesse,  Gunnison  Co.,  Colorado, 
and  in  small  amounts  at  Franklin,  N.  J.,  Mine  La  Motte,  Mo.,  and  elsewhere.  A 
ferriferous  variety  occurs  in  gneiss  at  Chatham,  Conn. 

*  There  is  no  line  between  chloanthite  NiAs2  and  smaltite  CoAs2,  the  usual 
specimen  is  an  isomorphous  mixture.  The  Cobalt  district  mineral  is  such  a  mixture. 


292  MINERALOGY. 

ERYTHRITE. 

COMPOSITION. — Co3(AsO4)2.8H2O,  (CoO  37.5,  As2O5  38.4,  H2O  24.1  per  cent.). 

GENERAL  DESCRIPTION. — Groups  of  minute  peach  red  or  crimson  crystals  forming 
a  drusy  or  velvety  surface.  Also  in  small  globular  forms  or  radiated  or  as  an  earthy 
incrustation  of  pink  color. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  adamantine  or  pearly.  Color, 
crimson,  peach  red,  pink  and  pearl  gray.  Streak,  paler  than  color.  H.,  1.5.  to  2.5. 
Sp.  gr.,  2.91  to  2.95.  Flexible  in  laminae. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  easily,  evolves  white  fumes  with 
garlic  odor,  and  leaves  a  magnetic  residue,  which  imparts  the  characteristic  blue  to 
borax  bead.  Soluble  in  hydrochloric  acid  to  a  light  red  solution. 

Asbolane  or  asbolite  is  essentially  a  mixture  of  oxides  of  manganese  and  cobalt 
and  is  grouped  under  wad,  p.  283.  The  asbolane  from  the  lateral  secretion  veins  in 
serpentine  in  New  Caledonia  has  been  an  important  source  of  cobalt. 

MILLERITE.  —  Capillary  Pyrites. 

COMPOSITION.  —  NiS,  (Ni  64.4  per  cent.). 

GENERAL  DESCRIPTION.  —  A  brass-colored  mineral  with  metallic 
lustre,  especially  characterized  by  its  occurrence  in  hair-like  or 
needle  crystals,  often  interwoven  or  in  crusts  made  up  of  radiating 
needles. 

Physical  Characters.     H.,  3  to  3.5.     Sp.  gr.,  5.3  to  5.65. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  greenish-black.  TENACITY,  crystals  elastic. 

COLOR,  brass  or  bronze  yellow. 

BEFORE  BLOWPIPE,  ETC.^-On  charcoal  spirts  and  fuses  to  a 
brittle  magnetic  globule,  which  will  color  borax  red.  Soluble  in 
aqua  regia  to  a  green  solution,  yielding  with  dimethy'glyoxime 
the  characteristic  crimson  precipitate. 

REMARKS. — Millerite  occurs  as  a  magmatic  segregation  with  nickeliferous  pyrrho- 
tite  at  Gap  Mines,  Pa.,  as  needle  crystals  in  cavities  of  other  minerals  such  as  hema- 
tite (Antwerp,  N.  Y.),  dolomite  (near  St.  Louis,  Mo.),  chalcopyrite  (Baden),  or  in 
ore  veins,  especially  with  iron,  cobalt,  nickel  and  bismuth  minerals. 

PENTLANDITE. 

COMPOSITION. — (Fe.Ni)S.  Sudbury  average  of  five  analyses 
Ni  35-57»  Co  0.83,  Fe  29.06,  S  33.25  per  cent. 

GENERAL  DESCRIPTION. — Light  bronze-yellow,  granular  masses 
of  metallic  lustre.  Octahedral  cleavage.  Color  of  fresh  fracture 
that  of  pyrrhotite  but  tarnishes  to  more  brassy  yellow. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.      293 

Physical  Characters.     H.,  3.5  to  4.     Sp.  gr.,  4.6  to  5. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  black.  TENACITY,  brittle. 

COLOR,  light  bronze  yellow.  NOT  MAGNETIC. 

BEFORE  BLOWPIPE,  ETC. — Fuses  readily  to  a  magnetic  globule 
which  gives  bead  tests  for  nickel.  Soluble  in  nitric  acid,  the 
solution  yielding  with  dimethyl-glyoxime  the  characteristic  crim- 
son precipitate. 

REMARKS. — Occurs  as  the  important  nickel  mineral  in  the  nickel-pyrrhotite 
magmatic  segregation  at  Sudbury,  Ontario.  It  occurs  also  at  Lillehammer,  Nor- 
way, with  chalcopyrite. 

NICCOLITE.— Copper  Nickel. 

COMPOSITION. — NiAs,  (Ni  43.9  per  cent.).  As  is  replaced  to 
some  extent  by  Sb  or  S,  and  Ni  by  Fe  or  Co. 

GENERAL  DESCRIPTION. — A  massive  mineral  of  metallic  lustre, 
characteristic  pale  copper  red  color  and  smooth  impalpable  struct- 
ure. Sometimes  the  copper-red  kernel  has  a  white  metallic  crust. 
Occasionally  occurs  in  small  indistinct  hexagonal  crystals. 

Physical  Characters.     H.,  5  to  5.5.     Sp.  gr.,  7.3  to  7.67. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  brownish-black.  TENACITY,  brittle. 

COLOR,  pale  copper  red  with  dark  tarnish. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  easily,  giving  off 
white  fumes  with  garlic  odor  and  leaving  a  magnetic  residue,  which 
will  color  borax  bead  red  and  sometimes  blue,  in  which  case  the 
borax  must  be  renewed  until  the  cobalt  is  all  removed.  In 
open  tube  yields  a  white  sublimate  and  a  yellowish-green  pul- 
verulent residue.  Soluble  in  concentrated  nitric  acid  to  a  green 
solution,  which  may  be  tested  as  under  millerite. 

SIMILAR  SPECIES. — Differs  from  copper  in  hardness,  black  streak 
and  brittleness. 

REMARKS. — Occurs  principally  in  ore  veins  in  the  crystalline  schists,  often  with 
silver  ores  as  in  the  Saxon  mines  and  many  other  European  localities.  Occurs  in 
considerable  quantity  at  la  Rioja,  Argentina,  and  Albergera  Velha,  Portugal.  The 
principal  American  locality  is  at  Cobalt,  Ont.  It  is  also  found  at  Lovelock's,  Nevada; 
Tilt  Cove,  Newfoundland;  Chatham,  Conn.;  and  Thunder  Bay,  Lake  Superior. 


294  MINERALOGY. 

ANNABERGITE.— Nickel  Bloom. 

COMPOSITION. — Ni3(AsO4)2.8H2O,  (NiO  37.4  As2O5  38.5,  H2O  24.1  per  cent.). 

GENERAL  DESCRIPTION. — Pale  apple-green  crusts,  and  occasionally  very  small 
hair-like  crystals.  Usually  occurs  on  niccolite  or  smaltite. 

PHYSICAL  CHARACTERS. — Dull.  Color,  apple-green.  Streak,  greenish-white. 
H.,  i. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses  easily  to  a  magnetic  button,  and  be- 
comes dull  and  yellow  during  fusion,  evolving  garlic  odor.  In  closed  tube,  yields 
water  and  darkens.  With  borax,  gives  red  bead.  Soluble  in  nitric  acid. 

REMARKS. — Results  from  the  weathering  of  niccolite  or  smaltite  and  is  usually 
found  incrusting  these  minerals  though  sometimes  massive  as  at  Churchill  Co., 
Nevada;  and  Reichelsdorf,  Silesia. 

GARNIERITE.— Noumeite. 

COMPOSITION. — H2(Ni.Mg)SiO4  +  H2O?  very  variable. 

GENERAL  DESCRIPTION. — Loosely  compacted  masses  of  brilliant 
dark-green  to  pale-green  mineral,  somewhat  unctuous.  Structure 
often  small  mammelonated,  with  dark-green,  varnish-like  surfaces, 
enclosing  dull  green  to  yellowish  ochreous  material.  Easily 
broken  and  earthy. 

Physical  Characters.     H.,  2  to  3.    Sp.  gr.,  2.27  to  2.8. 
LUSTRE,  varnish-like,  to  dull.  OPAQUE. 

STREAK,  light  green  to  white.  TENACITY,  fr'able. 

COLOR,  deep  green  to  pale  greenish-white. 
UNCTUOUS,  adheres  to  the  tongue. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  decrepitates  and  becomes 
magnetic.  In  closed  tube  yields  water.  Borax  bead  gives  nickel 
reaction.  Partially  soluble  in  hydrochloric  and  nitric  acids. 

SIMILAR  SPECIES. — Differs  from  malachite  and  chrysocolla  in 
structure  and  unctuous  feeling.  Differs  from  serpentine  in  deep 
color  and  nickel  reaction. 

REMARKS. — Occurs  as  described  on  p.  289,  in  lateral  secretion  veins  in  serpentine* 
in  Noumea,  New  Caledonia,  derived  from  a  peridotite.  Also  from  similar  weathering 
of  a  peridotite  at  Riddles,  Oregon.  A  similar  large  deposit  is  reported  in  Malaga, 
Spain. 

USES. — Next  to  the  nickel-pyrrhotites  it  is  now  the  most  im- 
portant source  of  nickel. 

*  At  Locris,  near  Athens,  a  dull  brown  7  per  cent.  NiO  ore  occurs  and  in  eastern 
Cuba  there  are  vast  deposits  of  limonite  carrying  0.8  per  cent,  of  nickel  and  cobalt, 
both  deposits  apparently  due  to  decay  of  peridotites. 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.      295 


Sphalerite 

Wurtzite 
Goslarite 
Zincite 
Smithsonite 
Hydrozincite 
Aurichalcite 
Willemite 
Calamine 
Franklinite 
Gahnite 

ZnS 
ZnS 
ZnSO4.7H2O 
ZnO 
ZnCO3 
ZnCO3.2Zn(OH)2 
(Zn,  Cu)6(C03)2(OH)« 
Zn2Si04 
(ZnOH)2Si03 
(Zn,  Mn)Fe2O4 
ZnAl2O4 

Isometric 
Hexagonal 
Orthorhombic 
Hexagonal 
Hexagonal 

Hexagonal 
Orthorhombic 
Isometric 
Isometric 

The  name  GENTHITE  has  been  used  for  green  nickeliferous  magnesium  silicates 
of  very  varying  composition  which  occur  coating  chromite  at  Lancaster  Co.,  Pa., 
and  forming  a  layer  in  sandstone  in  Webster  Co.,  N.  C.,  and  the  name  PIMELITE 
for  a  similar  material  with  more  alumina  from  Frankenstein,  Silesia. 

THE  ZINC   AND   CADMIUM   MINERALS. 

The  zinc  minerals  described  are: 

Sulphides 

Sulphate 

Oxide 

Carbonates 


Silicates 


Aluminates  and  Ferrates 


The  cadmium  mineral  described  is: 

Sulphide  Greenockite  CdS.  Hexagonal 

ECONOMIC  IMPORTANCE. 

The  important  ores  of  zinc  are  sphalerite,  smithsonite,  and  cala- 
mine;  and,  in  New  Jersey,  willemite,  zincite  and  franklinite. 

Cadmium  is  not  obtained  directly  from  greenockite  but  from 
zinc  ores. 

In  this  country,  Missouri  and  New  Jersey  have  for  years 
yielded  most  of  the  zinc  ore  but  the  development  of  the  "flotation" 
processes  has  made  new  centers  of  zinc  production,  such  as  Mon- 
tana and  Idaho,  and  the  ores  of  Colorado  and  Oklahoma  have  come 
into  the  market.*  In  all,  in  1915,  this  country  produced  492,495 
tons  of  metallic  zinc. 

More  complete  statistics  for  1914,  exclusive  of  secondary  zinc,  recovered  from 
old  brass  and  zinc  articles,  give  in  short  tons: 

Manufactured.  Imported.  Exported. 

Metallic  Zincf 353,049  860  64,802 

Zinc  in  Zinc  Pigments 70,619  2,629$  15, 

Zinc  Dust 1,003  2,004 

*  By  states  in  1914  the  yield  in  tons  of  contained  zinc  was  in  the  order: 


Missouri 105,994 

New  Jersey 74,253 

Montana 55.79O 

Colorado 48,387 


Wisconsin 31,113 

Idaho 21,106 

Oklahoma 13,992 

Kansas 11,284 


Mineral  Resources  of  U.  S.,  1914,  Vol.  2,  p.  877. 
f  Of  this,  9,631  from  foreign  ores.          J  Oxide. 


296  MINERAL  OGY. 

Metallic  zinc  is  obtained  by  distillation  of  its  roasted  ores  with 
carbon.  The  sulphide  and  carbonate,  by  roasting,  are  converted 
into  oxide,  and  the  silicates  are  calcined  to  remove  moisture.  The 
impure  oxides,  or  the  silicates,  are  mixed  with  fine  coal  and  charged 
in  tubes  or  vessels  of  clay,  closed  at  one  end  and  connected  at  the 
other  end  with  a  condenser.  These  are  submitted  to  a  gradually 
increasing  temperature,  by  which  the  ore  is  reduced  to  metallic 
zinc,  and,  being  volatile,  distills,  and  is  condensed.  Apparently 
successful  processes  are  now  in  use  for  the  direct  deposition  of  zinc 
from  its  ores  by  electrolysis. 

The  principal  uses  of  metallic  zinc  are  in  galvanizing  iron  wire 
or  sheets  and  in  manufacturing  brass.  A  smaller  amount  is  made 
into  sheet  zinc. 

Zinc  oxide,  ground  in  oil,  constitutes  the  paint  zinc  white.  The 
oxide  may  be  made  from  the  metal  by  heating  it  to  a  temperature 
at  which  the  zinc  takes  fire  and  drawing  the  fumes  into  suitable 
condensers;  or,  as  in  this  country,  it  may  be  made  directly  from 
the  ore. 

Other  pigments,  also  in  this  country  made  directly  from  the  ore, 
are  "leaded  zinc  oxide,"  and  zinc  lead  oxide,  the  former  having 
more  lead  oxide. 

" Ltikophone"  an  intimate  mixture  of  ZnS  and  BaSO4  obtained 
by  chemical  precipitation  is  in  this  country  made  chiefly  from 
skimmings  and  scrap. 

The  world's  production  of  zinc  in  metric  tons  for  1913  was  estimated:* 

United  States 323,200               Great  Britain 59,ooo 

Germany 285,000               Holland 24,000 

Belgium 198,000               Russia 9,000 

France 70,000               Norway 8,000 

Zinc  Dust  results  if  the  retorts  cool  rapidly  below  the  freezing 
point  (about  418°  C.);  the  vapor  condenses  as  a  blue  powder 
containing  about  ten  per  cent,  of  ZnO.  It  is  extensively  used  in 
the  separation  of  gold  from  cyanide  solutions. 

Cadmium  is  obtained  almost  entirely  from  the  Upper  Silesian 
zinc  ores.  About  4^  metric  tons  were  so  obtained!  in  1914  of 
which  this  country  imported  1,239  pounds.  The  first  fumes  are 

*  Mineral  Industry,  1914,  p.  793. 
f  Mineral  Industry,  1914,  p.    82. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.      297 

redistilled  and  finally  reduced  with  carbon.  The  metal  is  used 
in  fusible  alloys  and  certain  forms  of  silver  plating.  The  sulphide 
forms  a  splendid  yellow  pigment  unaltered  by  exposure. 

FORMATION   AND    OCCURRENCE    OF    ZINC    ORES. 

There  seems  to  be  no  proof  of  any  frequent  occurrence  of  zinc 
in  igneous  rocks  even  in  minute  quantities.  A  few  analyses  indi- 
cate its  occasional  occurrence  and  Washington  states  that  there 
are  reasons  for  thinking  it  is  "  more  apt  to  be  present  in  acid  rocks." 

It  is  reported  in  traces  in  the  Triassic  sediments  of  Schwarzwald 
and  in  sea  water. 

The  occurrences  are  contact  deposits,  veins,  replacements  and 
residual  deposits. 

Contact  Deposits.* 

The  celebrated  deposit  at  Franklin  Furnace,  containing  willem- 
ite,  franklinite,  zincite,  is  probably  of  this  type  and  the  deposits 
at  Tres  Hermanas,  New  Mexico,  chiefly  willemite  and  the  Magda- 
lena  Mines,  New  Mexico  containing  much  sphalerite,  are  in  con- 
tact zones. 

Veins. 

Sphalerite  is  one  of  the  common  sulphides  of  the  mineral  veins. 

Replacements  in  Sedimentary  Rocks. 

The  most  important  zinc  deposits  of  the  world  occur  in  lime- 
stone, usually  with  lead,  and  possibly  concentrated  there  by  circu- 
lating waters  bearing  sulphate  solutions  from  which  the  zinc  was 
precipitated  principally  as  the  sulphide,  which  later  formed  car- 
bonate, smiihsonite  or  silicate  calcimine.  The  latter  are  usually 
above  the  sulphides.  At  Moresnet  the  oxidized  ores  extend  from 
the  surface  to  a  depth  of  200  to  300  feet,  the  sulphides  underlying. 
Similar  great  deposits  exist  in  Silesia;  Bleiberg,  Carinthia;  and  the 
Mississippi  Valley,  especially  near  Joplin,  Mo. 

Metasomatic  replacement  is  claimed  specifically!  for  Bleiberg, 
Carinthia,  Upper  Silesia,  part  of  Moresnetf  and  some  others. 
The  origin  of  the  zinc  solutions  is  disputed. 

*  Lindgren,  "  Mineral  Deposits,"  675  and  694. 

t  Beyschlag,  Vogt  and  Krusch,  Truscott's  translation,  42  and  183. 

t  Lindgren,  "Mineral  Deposits,"  416. 


298 


MINERALOGY. 


Residual  Deposits  of  smithsonite  and  calamine  as  at  the  Bertha 
Mines,  Va. 

SPHALERITE. — Blende,  Zinc  Blende,  Black-jack. 

COMPOSITION.  —  ZnS  (Zn,  67  per  cent).  Often  contains  Cd, 
Mn,  Fe. 

GENERAL  DESCRIPTION.  —  A  mineral  of  resinous  lustre  shading 
in  color  from  yellow  through  brown  to  nearly  black  and  trans- 
parent to  translucent  It  occurs  frequently  cleavable  massive  but 
also  in  crystals  and  in  compact  fine-grained  masses  or  alternate 
concentric  layers  with  galenite. 


FIG.  348. 


FIG.  349. 


FIG.  350. 


CRYSTALLIZATION. —  Isometric.  Hextetrahedral  class,  p.  62. 
Usually  the  dodecahedron  d  with  the  tetrahedron  p  and  a  modify- 
ing tristetrahedron  o  =  (a  :  30,  :  30);  {311!.  Fig.  349,  usually 
with  rounded  faces.  More  rarely  the  +  and  —  tetrahedron,  Fig. 
348  and  sometimes  in  twin  crystals  like  Fig.  350. 

Index  of  refraction  for  yellow  light,  2.3692. 

Physical    Characters.     H.,  3.5  to  4.     Sp,  gr.,  3.9  to  4.1. 
LUSTRE,  resinous.  TRANSPARENT  to  translucent. 

STREAK,  white  to  pale  brown.       TENACITY,  brittle. 
COLOR,  yellow,  brown,  black ;  rarely  red,  green  or  white. 
CLEAVAGE,  parallel  to  rhombic  dodecahedron  (angles   1 20°  and 

90°). 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  with  difficulty,  but 
readily  yields  a  sublimate,  sometimes  brown  at  first  from  cadmium 
and  later  yellow  while  hot,  white  when  cold  and  becoming  bright 
green  if  moistened  and  ignited  with  cobalt  solution.  With  soda 
gives  a  sulphur  reaction.  Soluble  in  hydrochloric  acid  with  effer- 
vescence of  hydrogen  sulphide. 

SIMILAR  SPECIES. — Smaller  crystals  sometimes  slightly  resemble 
garnet  or  cassiterite,  but  are  not  so  hard. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.      299 

REMARKS. — The  occurrences  are  as  stated  on  p.  297.  It  is  obtained  largely  as 
concentrates  in  southwest  Missouri,  Wallace,  Idaho;  Kansas,  Miami,  Oklahoma, 
at  Friedensville,  Pa.,  in  the  southwestern  part  of  Wisconsin,  at  Pulaski,  Va.,  and 
at  many  other  places.  In  small  quantities  it  is  of  very  common  occurrence. 

WURTZITE. — ZnS,  found  in  small  hexagonal  crystals  at  Joplin,  Mo.  (prism 
and  base),  and  Butte,  Mont,  (pyramidal).  Also  occurs  in  concentric  layers  of  radiat- 
ing fibers  (Schalenblende)  with  sphalerite  at  Pribram,  Bohemia;  Pontpeau,  France; 
Liskeard,  Cornwall.  The  Schalenblende  of  Geroldseck,  Baden,  is  all  wurtzite.  In 
physical  and  blowpipe  tests  essentially  like  sphalerite. 

GOSLARITE.— Zinc  Vitriol.  ZnSO4.7H2O,  is  formed  by  the  oxidation  of 
sphalerite  in  damp  locations.  It  is  a  white  or  yellowish  earthy  mineral  with  nauseous 
astringent  taste.  Usually  an  incrustation  or  mass  shaped  like  the  original  sphalerite 
or  in  stalactites.  Rarely  needle-like  orthorhombic  crystals.  Goslarite  is  formed 
by  the  oxidation  of  sphalerite,  especially  in  the  presence  of  iron  sulphides.  Its 
interesting  feature  is  that  many  great  zinc  deposits  appear  to  have  been  precipitated 
from  sulphate  solutions. 


ZINCITE.— Red  Zinc  Ore. 

COMPOSITION. — ZnO,  (Zn  80.3  per  cent.)  with  usually  some  Mn 
or  Fe. 

GENERAL  DESCRIPTION. — A  deep  red  to  brick-red  adamantine 
mineral  occurring  in  lamellar  or  granular  masses,  either  in  calcite 
or  interspersed  with  grains  and  crystals  of  black  franklinite  and 
yellow  to  green  willemite.  A  few  hexagonal  pyramids  have  been 
found. 
Physical  Characters.  H.,  4  to  4.5.  Sp.  gr.,  5.4  to  5.7. 

LUSTRE,  sub-adamantine.  TRANSLUCENT. 

STREAK,  orange  yellow.  TENACITY,  brittle. 

COLOR,  deep  red  to  orange  red. 

CLEAVAGE,  basal  and  prismatic  yielding  hexagonal  plates. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  On  charcoal  gives  reactions 
for  zinc  as  described  under  sphalerite.  In  closed  tube  blackens,  but 
is  again  red  on  cooling.  With  borax  usually  gives  amethystine 
bead.  Soluble  in  hydrochloric  acid  without  effervescence. 

SIMILAR  SPECIES. — Differs  from  realgar  and  cinnabar  in  its  asso- 
ciates, infusibility  and  slow  volatilization. 

REMARKS. — Occurs  at  Sterling  Hill,  near  Ogdensburgh,  and  Mine  Hill,  near 
Franklin  Furnace,  N.  J.,  constituting  only  about  one  half  per  cent,  of  the  average 
ore.  Also  in  small  amounts  in  Schneeberg,  Saxony;  the  lead  mines  of  Tuscany; 
Olkusz,  Poland,  and  elsewhere. 


300  MINERAL  OGY. 

SMITHSONITE.  —  Dry  Bone,  Calamine. 

COMPOSITION.  —  ZnCO3  (ZnO,  64.8  ;  CO2,  35.2  per  cent). 

GENERAL  DESCRIPTION.  —  Essentially  a  white  vitreous  mineral 
but  often  colored  yellowish  or  brownish  by 
iron.  Structure  stalactitic  or  botryoidal,  or 
with  drusy  crystal  surface ;  also  in  porous 
cavernous  masses  and  granular.  Sometimes 
of  decided  colors,  as  deep  green  or  bright  yel- 
low, from  copper  or  cadmium  respectively. 

CRYSTALLIZATION. — Hexagonal.     Scaleno- 
hedral  class,  p.  48.     Axis  c  =  0.8063.     Usually 
small  rhombohedrons  of  73°,  Fig.  351,  like  those  of  siderite. 

Optically — . 

Physical  Characters.     H.,  5.     Sp.  gr.,  4.3  to  4.5. 

LUSTRE,  vitreous  to  dull.  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  shades  of  white,  more  rarely  yellow,  green,  blue,  etc. 
CLEAVAGE,  parallel  to  rhombohedron  (107°). 

BEFORE  BLOWPIPE,  ETC. — Infusible  but  readily  yields  white 
sublimate  on  coal,  often  preceded  by  brown  of  cadmium.  The 
sublimate  becomes  yellow  when  heated  and  becomes  bright  green 
when  moistened  with  cobalt  solution  and  then  heated.  Soluble 
in  acids  with  effervescence. 

SIMILAR  SPECIES. — Distinguished  from  calamine  by  its  efferves- 
cence and  from  other  carbonates  by  its  hardness. 

REMARKS. — Occurs  secondary  after  sphalerite  as  a  replacement  of  limestone  or 
dolomite,  and  as  residual  material.  The  many  zinc  deposits  usually  consist  in  their 
upper  portions  of  smithsonite  and  calamine;  this  is  the  case  at  Moresnet,  Silesia, 
many  of  the  deposits  of  the  Mississippi  Valley,  and  the  Magdalena  District,  New 
Mexico. 

HYDROZINCITE.— Zinc  Bloom. 

COMPOSITION.— ZnCO3'2Zn(OH)2,     (ZnO  75.3,  C02  13.6,  H2O  ii.i  per  cent.). 

GENERAL  DESCRIPTION. — Usually  a  soft  white  incrustation  upon  other  zinc  minerals, 
or  as  dazzling  white  stalactites,  or  earthy  and  chalk  like. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  dull  or  pearly.  Color,  pure  white  to 
yellowish.  Streak  shining  white.  H.,  2  to  2.5.  Sp.  gr.,  3.58  to  3.8. 

BEFORE  BLOWPIPE,  ETC.  —  Infusible.  Coats  the  coal  like  smithsonite.  Yields 
water  in  closed  tube.  Soluble  in  cold  dilute  acids  with  effervescence. 

REMARKS. — Hydrozincite  results  from  the  alteration  of  other  zinc  ores  and  occurs 
in  minor  quantities  in  many  zinc  deposits.  Larger  quantities  have  been  found  at 
Santander,  Spain;  Raibl,  Carinthia  and  Constantine,  Algeria. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.      301 


AURICHALCITE,  (Zn,  Cu)5(CO  )2(OH)6,  in  pale  bluish  green  and  often  velvety 
incrustations  often  on  smithsonite.  Sometimes  pearly  imperfect  crystals.  H  =  2, 
Sp.  gr.,  3.54  to  3.64. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  colors  flame  green  and  yields  white  coating 
made  green  by  moistening  with  cobalt  solution  and  igniting.  Soluble  in  acids  with 
effervescence. 

REMARKS. — Occurs  in  Zacatecas,  Mexico;  Salt  Lake  Co.,  Utah;  Santa  Caterina, 
Arizona;  Laurium,  Greece;  Rezbanya,  Hungary;  and  many  other  localities. 

WILLEMITE.— Troostite. 

COMPOSITION. — Zn2SiO4,  (ZnO,  72.9;  SiO2,  27.1);  often  with 
much  manganese  replacing  zinc. 

GENERAL  DESCRIPTION. — Compact,  translucent,  somewhat  res- 
inous material,  yellow  or  greenish  or  brownish  red  in  color,  often 
mottled;  granular  mixtures  with  black  frank-  FIG.  352. 

linite;    transparent    and    opaque     prismatic 
crystals  often   large   (Franklin,  N.   J.),   Fig. 

352. 

Brown,  granular  masses  with  minute  crys- 
tals (Altenberg,  Belgium). 

Dark  gray  cellular  masses  with  radial  ag- 
gregates of  slender  crystals  (Tres  Hermanas, 
New  Mexico). 

CRYSTALLIZATION. — Hexagonal.  Class  of  third  order  rhombo- 
hedron,  p.  54.  Axis  c=  0.6775.  p=  {ioi~i},e=  {oil2},a 
=  {1120}.  Supplement  angles  are  pp  =  64°  30';  ee  =  36°  47'. 

Physical  Characters.     H.,5.     Sp.  gr.  3.89  to  4.2. 

LUSTRE,  resinous.  TRANSPARENT  to  opaque. 

STREAK,  nearly  white.  TENACITY,  brittle. 

COLOR,  greenish  to  sulphur  yellow,  apple  green,  white,  flesh  red, 
gray,  brown  and  blue. 

REMARKS. — Occurs  as  the  result  of  contact  metamorphism  (presumably  of  cala- 
mine)  in  its  two  most  important  localities,  Sussex  County,  New  Jersey,  and  Tres 
Hermanas,  New  Mexico.  Also  found  in  Altenberg  near  Moresnet  in  a  layer  with 
calamine  and  smithsonite;  and  in  Stolberg  in  veins.  From  Greenland  blue  colored 
crystals  are  reported,  and  it  has  been  recognized  at  Socorro,  New  Mexico,  and 
Clifton,  Arizona. 

CALAMINE.— Electric  Calamine. 

COMPOSITION.— (ZnOH)2SiO3,  (ZnO,  67.5  ;  SiO3,  25.0;  H,O,  7.5 
per  cent.). 


302 


MINERALOGY. 


FIG.  353. 


Altenberg. 


GENERAL  DESCRIPTION — A  white  or  brownish  white  vitreous 
mineral  frequently  with  a  drusy  surface  or  in  radiated  groups  of 
crystals,  the  free  ends  of  which  form  a  ridge  or 
cockscomb,  also,  but  more  rarely,  small  distinct  trans- 
parent crystals.  It  occurs  also  granular,  stalactitic, 
botryoidal  and  as  a  constituent  of  some  clays. 

CRYSTALLIZATION. —  Orthorhombic.  Hemimorphic 
class,  p.  41.  Axes  a  :  &  :  c  —  0.783  ;  i  :  0.478.  The 
crystals  are  usually  tabular,  the  broad  face  being  the 
brachypinacoid  b,  while  the  prism  m  is  relatively 
small,  v  is  the  pyramid  2d  :  b  :  2c  ;  {121}. 

Optically  +,  with  acute  bisectrix  vertical.      2E  for 
yellow  light  =  78°  39'. 

Physical  Characters.         H.,  4.5  to  5.     Sp.  gr.,  3.4  to  3.5. 

LUSTRE,  vitreous  to  pearly.  OPAQUE  to  transparent. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  yellow  to  brown,  white,  colorless,  rarely  blue  or  green. 

BEFORE  BLOWPIPE,  ETC. — Fusible  only  in  finest  splinters.  With 
soda  and  borax,  on  charcoal  yields  a  white  coating,  which  is  made 
bright  green  by  heating  with  cobalt  solution.  In  closed  tube, 
yields  water.  With  acids,  dissolves,  leaving  a  gelatinous  residue. 

SIMILAR  SPECIES. — It  is  softer  than  prehnite,  harder  than  cerus- 
site,  and  gelatinizes  with  acids.  It  differs  from  willemite  in  water 
reaction,  and  from  stilbite  in  difficulty  of  fusion. 

REMARKS. — Occurs  usually  with  smithsonite  in  upper  portions  of  the  great  zinc 
replacement  deposits,  p.  297,  or  as  residual  material.  Sometimes  forms  separate 
deposits  as  at  Herbesthal,  Belgium,  or  may  be  with  hydrozincite  as  at  Cumillas 
Santander,  Spain.  In  this  country  it  has  been  mined  at  Granby,  Mo.,  Sterling  Hill, 
N.  J.,  Bertha,  Va.,  and  various  localities  in  Tennessee,  Arkansas  and  Nevada. 


FRANKLINITE. 

COMPOSITION.  —  (Fe.Mn.Zn)  (Fe.Mn)2O4. 

GENERAL  DESCRIPTION.  —  A  black  mineral  re- 
sembling magnetite.  Occurs  in  compact  masses, 
rounded  grains  and  octahedral  crystals.  Only 
slightly  magnetic  and  generally  with  brown 
streak.  The  red  zincite  and  yellow  to  green 
willemite  are  frequent  associates.  The  crystals 
are  modified  octahedrons  rarely  sharp  cut  as  in  magnetite 


FIG.  354- 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.      303 

Physical  Characters.  —  H.,  6  to  6.5.     Sp.  Gr.,  5  to  5.2. 

LUSTRE,  metallic  or  dull.  OPAQUE. 

STREAK,  brown  to  black.  TENACITY,  brittle. 

COLOR,  black.  Breaks  parallel  to  octahedron. 

Slightly  magnetic  at  times. 

BEFORE  BLOWPIPE,  ETC.— Infusible.  On  charcoal  with  soda 
gives  white  coat  of  zinc  oxide.  In  beads  gives  manganese  reaction. 
Slowly  soluble  in  hydrochloric  acid  with  evolution  of  some  chlorine. 

SIMILAR  SPECIES. — Distinguished  from  magnetite  and  chromite 
by  bead  tests  and  associates. 

REMARKS. — The  only,  noteworthy  locality  is  that  in  the  vicinity  of  Franklin  Fur- 
nace, New  Jersey.  Here,  however,  the  deposit  is  large  and  has  been  extensively 
developed. 

USES. — The  zinc  is  recovered  as  zinc  white  and  the  residue  is 
smelted  for  spiegeleisen  an  alloy  of  iron  and  manganese  used  in 
steel  manufacture.  Franklinite  has  also  been  ground  for  a  dark 
paint. 

GAHNITE. — Zinc  Spinel,  ZnAl2C»4.  Octahedral  crystals  of  green  to  black  color. 
Usually  opaque  and  vitreous  and  with  gray  streak.  H.,  7.5  to  8.  Sp.  gr.,  4  to  4.6. 
On  charcoal  infusible  but  gives  the  coating  of  zinc  oxide.  Occurs  in  talcose  schist 
at  Falun,  Sweden,  in  greenish  crystals  in  Calabria,  etc.,  and  in  this  country  especially 
with  franklinite  and  willemite  at  Franklin  Furnace,  N.  J.,  and  with  pyrite  at  Rowe, 
Mass. 

GREENOCKITE. 

COMPOSITION.— CdS,     (Cd,  77.7  per  cent.) 

GENERAL  DESCRIPTION. — Usually  a  bright  yellow  powder  upon  sphalerite,  or  a 
yellow  coloration  in  smithsonite.  Very  rarely  as  small  hemimorphic  hexagonal  crys- 
tals. ^  =  0.81 1 1. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre  earthy  01  adamantine.  Color  yel- 
low to  orange  yellow  or  bronze  yellow.  Streak  orange  yellow.  H.,  3  to  3.5.  Sp. 
gr.,  4.9  to  5.0. 

BEFORE  BIOWPIPE,  ETC. — Infusible,  but  is  easily  volatilized  in  the  reducing  flame, 
coating  the  coal  with  a  characteristic  brown  coat  and  a  iridescent  tarnish.  In  closed 
tube,  turns  carmine  red  on  heating,  but  is  yellow  on  cooling.  Soluble  in  strong 
hydrochloric  acid,  with  effervescence  of  hydrogen  sulphide. 

REMARKS. — Occurs  as  crystals  in  igneous  rocks  with  prehnite  at  Bishopstown, 
Scotland.  In  many  localities  it  occurs  incrusting  sphalerite*  as  at  Friedensville,  Pa., 
and  in  Missouri.  In  Marion  County,  Arkansas,  it  colors  smithsonite,  forming  the 
so-called  "turkey  fat"  ore. 

*  In  deposits  of  wurtzite  and  sphalerite  (Schalenblende)  the  greenockite  is  princi- 
pally in  the  wurtzite.  One  analysis  (Pribram)  showing  3.66  per  cent. 


304  MINER  A  LOG  Y. 

THE  TIN   MINERALS. 

The  minerals  described  are: 

Sulphide  Stannite  (Cu.Sn.Fe)S  Isometric 

Oxide  Cassiterite  SnO2  Tetragonal 

Staniferous  pyrite  occurs  in  the  Bolivian  mines  and  tin  is  also 
found  as  an  occasional  constituent  of  tantalite,  columbite,  and 
other  columbates  and  tantalates. 

It  is  also  an  essential  constituent  of  a  few  rare  species.* 

ECONOMIC   IMPORTANCE. 

Cassiterite  is  the  only  ore  of  tin,  and  while  deposits  exist  in  this 
country  (in  Virginia,  North  and  South  Carolina,  Dakota,  Alaska 
and  elsewhere,  the  product  for  1914  was  only  ore  from  Alaska, 
equivalent  to  104  tons  of  metallic  tin)  .f  The  world's  supply  of  tin, 
amounting  yearly  to  about  125,000  long  tons,  comes  chiefly  from 
the  East  India  islands  and  Bolivia. 

The  following  figures  are  given  for  1915:^ 

Long  Tons. 

Straits  and  Malay  Peninsula  (exports) 66,760 

Banka  and  Billiton  (sales) 15.093 

Bolivia  (exports) 18,800 

China  (exports  and  production) 7,097 

Cornwall  (production) 4,000 

Australia  (exports) 2,275 

South  Africa  (production) 2,158 

Nigeria 1,899 

118,082 

The  principal  use  of  tin  is  for  the  manufacture  of  tin  plate — 
sheet-iron  coated  with  tin — which  is  used  for  making  cans,  house- 
hold utensils,  etc.  Tin  is  also  largely  used  in  alloys,  such  as 
bronze,  bell  metal,  pewter,  solder  and  tin  amalgam.  Tinfoil  is  also 
made  from  it.  Large  quantities  of  sodium  stannate  are  used  in 
calico  printing. 

The  ore  as  mined  is  first  separated  from  gangue  and  impurities 
by  washing,  jigging,  etc.,  and  if  necessary,  is  then  calcined  or 
roasted,  to  remove  volatile  elements,  such  as  sulphur,  arsenic, 
antimony. 

*  Such  as  canfieldite,  franckeite,  kylindrite,  nordenskioldine. 

t  Mineral  Production  U.  S.,  1914,  Summary  by  H.  D.  McCaskey. 

}  Engineering  and  Mining  Journal,  1916,  p.  67. 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.      305 

The  concentrated  and  purified  ore  may  then  be  smelted  with 
carbon  in  a  shaft  furnace.  The  modern  practice  is,  however,  to 
smelt  the  ore  for  several  hours  in  a  reverberatory  furnace  with  coal. 
The  liquid  tin  is  drawn  off  and  the  slags  are  resmelted  at  a 
higher  temperature,  frequently  requiring  the  addition  of  iron  or  of 
lime  to  aid  in  the  separation  of  the  tin,  which  they  still  contain.  The 
impure  metal  obtained  is  slowly  heated  to  a  temperature  but  little 
above  the  melting  point  of  tin  ;  comparatively  pure  tin  separates 
and  this  is  further  purified  by  oxidation.  This  oxidation  is  accom- 
plished either  by  forcing  green  wood  under  the  liquid  metal  causing 
violent  agitation  or  by  repeatedly  pouring  the  melted  tin  in  a  thin 
stream  from  ladles.  Tin  may  also  be  refined  by  electrolysis. 

FORMATION   AND   OCCURRENCE   OF   TIN   DEPOSITS. 

Tin  oxide  occurs  in  granite*  in  amounts  rarely  exceeding  0.05 
per  cent,  and  occasionally  minute  crystals  of  cassiterite  are 
visible. 

In  granite  pegmatites,  cassiterite  is  sometimes  more  abundant 
as  in  the  Black  Hills,  South  Dakota.  In  Durango  and  Jalisco, 
Mexico,  it  occurs  in  a  rhyolitic  surface  flow.f 

The  primary  source  of  tin  therefore  is  an  acid  magma  and 
all  important  deposits  are  derived  from  such  magmas  by 
pneumatolytic  action,*  p.  242,  in  which  two  great  stages  are 
recognized. 

First,  extraction  from  the  acid  magma  by  aid  of  fluorine  and 
its  compounds,  the  tin  in  gaseous  state  exhaling  through  cracks 
in  the  crust  from  the  still  molten  interior  of  the  magma. 

Second.  The  deposition  in  the  fissures  and  in  the  country 
rock  and  the  conversion  of  the  latter  into  "greisen"§  by  the  intro- 
duction of  tin,  fluorine,  lithium  and  silica. 

*  Especially  in  the  mica,  but  also  in  the  feldspar. 

|  Lindgren  "Mineral  Deposits,"  p.  632. 

%  "  One  entire  class  of  deposit,  that  of  the  tin  lodes,  owes  its  existence  entirely  to 
the  action  of  these  gases  and  vapors  either  between  themselves  or  upon  the  rocks 
with  which  they  come  in  contact."  Beyschlag,  Vogt  and  Krusch,  "Ore  Deposits," 

P-  174- 

§  Coarse-grained   rocks  consisting  of   quartz,    mica,    topaz,   or  tourmaline  and 
cassiterite.     For    the    Erzgebirge,    Lindgren    quotes:  Quartz    50.28,    topaz    12.14, 
lithia,  mica,  36.80,  cassiterite  0.43,  "Mineral  Deposits,"  p.  620. 
21 


306  MINERAL  OGY. 

Tin  Veins. 

The  great  deposits  are  veins  or  lodes  in  or  near  granite  such  as 
the  long-worked  deposits  of  the  Saxon  and  Bohemian  Erzgebirge 
and  of  Cornwall  and  Devon,  England. 

The  great  deposits  of  Mt.  Bischof,  Tasmania,  are  in  "intensely 
altered"*  porphyritic  dikes  but  derived  from  the  same  magma  as 
a  distant  granite  mass. 

The  veins  worked  in  the  "straits"  are  in  limestone  but  sur- 
rounded by  granite  hills. 

The  Bolivian  veins  at  Oruro  contain  silver  minerals  and  much 
pyrite,  but  the  pneumatolytic  action  is  indicated  by  the  abundant 
tourmaline  in  the  country  rock. 

Contact  Deposits. 

The  contact  deposits  at  Pitkaranta,  Finland,  include  not  only 
copper  and  iron  ores  but  cassiterite  with  microscopic  topaz  and 
with  scheelite  and  fluorite. 

Residual  Deposits. 

The  erosion  and  weathering  of  tin  deposits  results  in  the  forma- 
tion of  placers  or  "gravels,"  some  just  below  the  outcrop  as  at 
Mt.  Bischoff,  Tasmania,  but  usually  further  from  the  parent  rock. 

The  weathering  removes  sulphides  and  the  gravels  yield  the 
purest  tin.  About  three  quarters  of  the  world's  supply  comes 
from  such  deposits,  chiefly  Malay  Peninsula,  Banka  and  Billiton, 
but  also  China,  Siam,  New  South  Wales  and  Alaska. 

STANNITE.— Tin  Pyrites. 

COMPOSITION. — (Cu.Sn.Fe)S.     Uncertain. 

GENERAL  DESCRIPTION. — A  massive,  granular  mineral,  of  metallic  lustre  and  steel- 
gray  color.  It  is  often  intermixed  with  the  yellow  chalcopyrite. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre  metallic.  Color  steel  gray  to  nearly 
black.  Streak  black.  H  =  4.  Sp  gr.,  4.5  to  4.52  Brittle. 

BEFORE  BLOWPIPE,  ETC. — In  the  reducing  flame  fuses.  In  the  oxidizing  flame 
yields  SO2,  and  is  covered  by  white  oxide,  which  becomes  bluish-green  when  heated 
with  cobalt  solution.  Soluble  in  nitric  acid  to  a  green  solution,  with  separation  of 
sulphur  and  oxide  of  tin.  With  soda,  gives  sulphur  reaction. 

REMARKS. — Stannite  occurs  in  comparatively  small  amount  in  the  tin  regions 
of  Cornwall,  Zinnwald  and  Bolivia.  In  this  country  it  has  been  found  at  the  Peerless 
Mine,  Black  Hills,  South  Dakota. 

*  Roughly  35  per  cent,  topaz,  65  per  cent,  quartz,  Beyschlag,  Vogt  and  Krusch, 
P-  445 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     307 

CASSITERITE.— Stream  Tin.    Tin  Stone. 

COMPOSITION. — SnO2,  (Sn  78.6  per  cent.),  and  usually  with  some 
Fe2O3,  and  sometimes  Ta2O5,  As2O6,  SiO2  or  Mn2O3. 

GENERAL  DESCRIPTION. — A  hard  and  heavy  brown  to  black 
mineral  occurring  either  in  brilliant  adamantine  crystals  or  more 
frequently  in  dullbotryoidal  and  kidney-shaped  masses  and  rounded 
pebbles,  often  with  a  concentric  or  fibrous  radiated  structure. 


FIG.  355- 


FIG.  356. 


FIG.  357- 


Stoneham,  Me. 


Cornwall,  Eng. 


Zinnwald. 


CRYSTALLIZATION.  —  Tetragonal.  Axis  c  =  0.672.  Common 
forms  are  the  unit  first  and  second  order  pyramids  and  prisms  p,  ar 
m,  and  d,  and  the  ditetragonal  pyramid  z  =  (a  :  \a  :  $c) ;  {321}. 
Supplement  angles  //  =  58°  19' ;  dd=  46°  28'  ;  mz  =  24°  59'. 

Frequently  twinned  parallel  to  the  second  order  pyramid,  Fig. 

357- 

Optically  +  with  high  indices  of  refraction  1.996  and  2.093. 

Physical  Characters.     H.,  6  to  7.     Sp.  gr.,  6.8  to  7.1. 
LUSTRE,  adamantine  to  dull.         OPAQUE  to  translucent 
STREAK,  white  or  pale  brown.       TENACITY,  brittle. 
COLOR,  brown  to  nearly  black,  sometimes  red,  gray,  or  yellow. 
CLEAVAGES,  indistinct  pyramidal  and  prismatic. 

BEFORE  BLOWPIPE,  ETC.  —  Infusible,  but  in  powder  becomes  yel- 
low and  luminous.  On  charcoal  with  soda  and  strong  heat  yields 
white  sublimate  which  is  made  bluish  green  by  heating  with 
cobalt  solution.  Insoluble  in  acids. 

The  uncrushed  mineral  placed  on  a  piece  of  zinc  in  dilute  hydro- 
chloric acid  is  coated  with  gray  metallic  tin. 
VARIETIES. 

Tin  Stone. — Crystals  and  granular  masses. 


308  MINERALOGY. 

Wood  Tin. — Masses  with  concentric  structure,  the  zones  being 
of  different  color  and  internally  fibrous. 

Stream  Tin. — Rounded  pebbles  and  grains  found  in  alluvial 
deposits. 

SIMILAR  SPECIES. — The  high  specific  gravity  distinguishes  it 
from  silicates  which  it  resembles,  and  the  infusibility  and  insolu- 
bility distinguish  it  from  wolframite,  etc. 

REMARKS. — In  America  the  chief  localities  are  Alaska;  Harney  Peak,  South 
Dakota;  Temescal,  California;  Gaffney,  South  Carolina;  and  Lincolnton,  North 
Carolina;  Shenandoah  Valley,  Virginia;  and  Durango,  Mexico.  It  has  been  found 
also  in  New  Hampshire,  Maine,  Massachusetts,  Alabama,  Wyoming  and  Montana. 

THE   TITANIUM   MINERALS. 

The  minerals  described  are : 

Oxides  Rutile  TiO2  Tetragonal 

Octahedrite  TiO2 

Brookite  TiO2  Orthorhombic 

Titanium  is  also  a  constituent  of  ilmenite  and  titanite,  and 
occurs  in  certain  varieties  of  common  silicates,  pyroxene,  amphi- 
bole,  mica,  garnet  (schorlomite),  chrysolite  as  well  as  in  a  number 
of  titanites  and  titanosilicates. 

ECONOMIC   IMPORTANCE. 

Although  the  ninth  in  quantity  of  the  elements  in  the  earth's 
crust,  titanium  has  few  uses.  The  production  for  1914  at  the 
Roseland,  Va.,  mines  was  equivalent  to  138  tons  of  titanic  oxide.* 
Oxide  of  titanium  is  used  to  impart  a  pinkish  color  to  artificial 
teeth  and  an  ivory-like  appearance  to  porcelain  and  from  it  titan- 
ium carbide  electrodes  for  arc  lights  are  made.  Ferrotitanium 
alloy  is  assuming  importance  as  a  deoxidizer  in  casting  steel  ingots 
for  rolling  mills.  Also  used  for  incandescent  lamp  filaments,  color- 
ing material  for  ceramics  and  various  salts  used  in  dyeing. 

FORMATION   AND    OCCURRENCE    OF    DEPOSITS. 

Titanium  Deposits. 

The  earth's  crust  contains  0.43  (Clarke)  per  cent,  of  titanium, 
much  of  which  is  in  the  magmatic  segregation  of  ilmenite  and 
titaniferous  magnetite  already  mentioned,  p.  263. 

Rutile  in  economic  quantities  is  also  .the  result  of  magmatic 
segregation  and  four  important  localities  exist: 

*  Mineral  Resources  of  the  U.  S.,  1914. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.     309 


In  Amhers^  and  Nelson  counties,  Va.,  in  syenite,  grading  into 
gabbro  and  with  gabbro  dikes. 

At  Kiagero,  Norway,  "streak-like"  in  granite  with  dikes  on 
both  sides. 

At  St.  Urbain's  Bay,  St.  Paul,  Canada,  where  the  ilmenite 
segregations  run  high  (up  to  20  per  cent.)  in  orange  red 
rutile. 

At  Mt.  Crawford,  So.  Australia,  where  rutile  crystals  in  economic 
quantity  can  be  washed  from  a  kaolinized  dike. 

RUTILE.— Nigrine. 

COMPOSITION. — TiO2,  (Ti  61  per  cent.). 

GENERAL  DESCRIPTION. — Brownish  red  to  nearly  black  pris- 
matic crystals  often  included  in  other  minerals  in  hair-like  or 
needle-like  penetrations.  Also  coarse  crystals  embedded  in  quartz, 
feldspar,  etc.,  or  in  parallel  and  crossed  and  netted  needles  upon 
hematite  or  magnetite.  Occasionally  massive  when  black  and  iron 
bearing. 


FIG.  358. 


FIG.  359. 


FIG.  360. 


Magnet  Cove,  Ark. 

CRYSTALLIZATION. — Tetragonal.  Axis  c  —  0.644.  Very  close 
to  cassiterite  in  angles  and  forms.  Usual  combinations  are  unit 
first  and  second  order  pyramids,  p  and  d,  and  first  and  second  order 
prisms,  m  and  a.  Often  twinned  in  knees,  Fig.  360,  and  rosettes, 
Fig.  359-  As  fine  hair-like  inclusions,  Fig.  216.  Prisms  often 
striated  vertically. 

Supplement  angles  pp  =  56°  52';  dd  =  45°  2'. 

Optically  +  with  very  high  indices  of  refraction  2.616  and  2.902 
for  yellow  light. 


310  MINERAL  OGY. 

Physical  Characters.     H.,  6  to  6.5,  Sp.  gr.,  4.15  to  4.25. 

LUSTRE,  adamantine  to  nearly  metallic.    OPAQUE  to  transparent. 

STREAK,  white,  pale  brown.  TENACITY,  brittle. 

COLOR,  reddish  brown,  red,  black,  deep  red  when  transparent. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  In  salt  of  phosphorus 
dissolves  very  slowly  in  the  oxidizing  flame  to  a  yellow  bead 
which  becomes  violet  in  the  reducing  flame.  Insoluble  in  acids. 

SIMILAR  SPECIES. — It  is  redder  and  of  lower  specific  gravity 
than  cassiterite.  The  nearly  metallic  lustre,  weight  and  infusi- 
bility  separate  it  from  garnet,  tourmaline,  vesuvianite,  and  pyrox- 
ene. 

REMARKS. — In  addition  to  the  magmatic  segregations  mentioned  rutile  occurs  as 
an  accessory  mineral  in  the  igneous  rocks,  in  the  sediments,  with  the  hardening  shales 
and  the  bauxite  deposits  and  in  the  metamorphic  rocks.  It  is  often  included  in 
quartz  and  feldspar. 

In  this  country  notable  localities  are  Graves  Mt.,  Ga.,  Magnet  Cove,  Ark.,  and 
Alexander  Co.,  N.  C. 

OCTAHEDRITE. — TiO2.  In  small  pyramidal  tetragonal  crystals  c  =  1.777. 
Either  black  opaque  and  nearly  metallic,  or  brown  translucent  and  adamantine. 

BROOKITE  =  TiO2.     Orthorhombic.     Axes  a  :  5  :  c  =  0.842  :  i  :  0.944. 

Either  brown  translucent  crystals  which  are  thin  and  tabular,  or  black  opaque 
crystals  of  varied  habit. 

ZIRCONIUM,  THORIUM,  CERIUM,  YTTRIUM  MINERALS. 

The  mineral )  described  are  : 

Oxide  Zirconium  oxide  ZrOz 

Phosphates  Monazite  (Ce,  La,  Di)PO4  Monoclinic 

Xenotime  Yt  PO4  Tetragonal 

Silicates  Zircon  ZrSiO4  Tetragonal 

Thorite  ThSiO4  Tetragonal 

Cerite  Hydrated  cerium  silicate  Orthorhombic 

Gadolinite  YtzI^FeSiaOio  Monoclinic 

Uranate  Thorianite  TM^.UsOs  Isometric 

These  elements  also  enter  into  a  large  series  of  silicates,  phos- 
phates and  niobates,  some  of  which  are  mentioned  in  footnotes 
of  the  succeeding  pages. 

Samars&ite,  fergusonite,  and  allanite,  are  described  in  this  book. 

ECONOMIC   IMPORTANCE. 

Zirconium. 

The  metal  has  no  uses.  The  oxide  zirconia  glows  brilliantly 
when  highly  heated  and  is  very  durable.  It  is  used  for  coating 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.     311 

the  cylinders  of  the  Drummond  light  and  the  filament  of  the  Nernst 
light  is  chiefly  zirconia  with  less  yttria  and  other  rare  earths.  A 
recent  larger  use  is  as  the  "  opacifier  "  in  the  white  glass  used  in 
indirect  electric  lighting.  The  chief  source  is  the  Brazilian  zir- 
conium oxide.  The  zircon  of  Norway  and  of  North  and  South 
Carolina  were  formerly  important  sources. 

The  zirconia  is  made  from  zircon*  or  altered  zircon  (zirconium  oxide)  by  fusing 
with  acid  potassium  fluoride,  extracting  with  hot  water,  treating  with  hydrochloric 
acid  and  precipitating  with  ammonia. 

Thorium. 

The  metal  and  its  alloys  have  no  economic  uses.  The  oxide, 
thoria,  is  very  important  because  of  its  use  in  different  incandescent 
gas  mantles.  The  mantle  of  the  Welsbach  lamp  consists  of  about 
99  per  cent,  of  thoria  with  one  per  cent,  of  ceria. 

Thoria  is  manufactured  by  methods  which  are  carefully  guarded.  In  practice 
monazite  as  it  comes  into  the  markets  is  separated  from  other  impurities  which 
occur  in  the  sand  by  means  of  Wetherill  magnetic  separators.  This  monazite  is 
then  treated  with  strong  sulfuric  acid'  and  the  thorium  later  precipitated. 

Both  thorite}  and  ihorianite  are  used  for  the  manufacture  of 
thoria,  but  the  supply  is  limited. 

The  chief  source  is  the  cerium  mineral,  monazite,  of  which  it  is 
stated  about  3000  tons  per  year  are  used.  Monazite  carries 
salts  of  thorium  as  impurities  and  in  quantities  varying  from 
traces  to  as  much  as  18.5  per  cent,  of  thorium  oxide. 

Brazil  furnishes  most  of  the  monazite  although  Travancore, 
Madras,  in  1912  produced  1,135  tons,  containing  14  per  cent, 
thoria  and  Ceylon  224  Ibs.  thorianite  in  1910. 

Cerium. 

Metallic  cerium  is  an  important  part  of  the  alloy  called  "Misch 
metal"  made  from  residues  after  removal  of  thoria.  It  is  used 
as  a  reducing  agent  and  is  said  to  be  the  alloy  in  patent  cigar 
lighters. 

The  oxide  ceria  is  used  in  various  incandescent  mantles  and  the 

*  A  few  of  the  other  species  containing  zirconium  are  wohlerite,  eudialite,  naegite, 
zirkelite  and  lavenite. 

t  The  following  minerals  also  are  usually  rich  in  thorium  and  would  be  valuable  if 
found  in  quantity:  Thorogummite,  mackintoshite,  aeschynite,  zirkelite,  tscheffkinite, 
yttrialite,  caryocerite,  euxenite,  pyrochlore. 


312  MINERALOGY. 

fluoride  in  the  flaming  arc  light.     Other  compounds  are  used  in 
making  and  fixing  dyes  and  in  color  photography. 

Cerite  is  made  directly  into  a  crude  sulphate  used  as  a  catalyst 
in  sulphuric  acid  manufacture. 

The  manufacture  of  the  oxide  is  incidental  to  the  manufacture  of  thoria.  No 
mineral  is  used  exclusively  for  making  ceria.*  Monazite  is  the  principal  source.f 

Yttrium. 

The  oxide  yttria,  Y2O3,  was  used  in  the  Nernst  lamp  filament 
and  in  gas  mantles. 

Gadolinite\  is  the  chief  mineral,  though  yttria  may  be  recovered 
in  any  separation  of  the  groups. 

FORMATION  AND   OCCURRENCE   OF  ZIRCONIUM,  THORIUM,   CERIUM 
AND   YTTRIUM    DEPOSITS. 

These  elements  occur  in  the  igneous  rocksj  and  certain  gneisses. 
Zirconium  is  the -most  plentiful,  but  cerium  and  yttrium  are 
estimated  at  only  o.ooi  per  cent,  and  thorium  at  only  o.oooi 
per  cent. 

The  economic  deposits  are  practically  limited  to  pegmatites  of 
granite  or  syenite,  such  as  those  of  southern  Norway  and  Sweden 
or  Baringer  Hill,  Texas  and  to  residual  deposits  such  as  the 
monazite  sands  of  Brazil  or  the  gold  washings  of  Henderson 
County,  N.  C.,  and  the  "  zircon  favas"  (Favas  =  rounded  pebbles) 
bearing  gravels  of  Minas  Geraes,  Brazil.  A  sandstone  carrying 
12  to  29  per  cent,  of  zircon  occurs  near  Ashland,  Va. 

ZIRCONIUM    OXIDE. 

Zirconium  oxide,  ZrO2,  occurs  in  negligible  quantities  as  the  mineral  baddeleyite, 
of  which  a  crystal  fragment  (monoclinic)  was  found  in  the  Ceylon  gem  gravels  at 
Rakwana,  and  it  has  been  found  at  Jacupiranga,  Brazil,  and  Alno,  Sweden,  in  basic 
(magnetite,  pyroxene,  chrysolite)  rocks.  The  oxide  is,  however,  found  in  quantity 
in  the  syenite  gravels  of  Serra  de  Caldas  and  Rio  Verdinho,  Minas  Geraes,  Brazil,  as 
masses  of  dark,  greenish  gray  color  with  fibrous  concentric  "Glaskopf"  structure 
resulting  from  decomposed  zircon  and  locally  known  as  "Zircon  Favas." 

*  A  few  of  the  many  other  species  carrying  cerium  are  tysonite,  parisite,  bast- 
naesite,  mosandrite,  tritomite,  fluocerite. 

t  Others  are  yttrfalite,  tengerite,  xenotime,  etc. 

%  Zircon,  monazite,  allanite  and  xenotime  are  most  frequently  observed. 


MINERALS   OF  METALLIFEROUS-  ORE    DEPOSITS.      313 


MONAZITE. 

COMPOSITION. — (Ce.La.Di)PO4,  but  with  notable  quantities  of 
thorium  and  silicon  and  frequently  small  amounts  of  erbium  and 
ytterbium. 

GENERAL  DESCRIPTION.  —  Small,  brown,  resinous  crystals,  or 
yellow,  translucent  grains,  disseminated  or  as  sand.  Sometimes  in 
angular  masses. 

CRYSTALLIZATION.  —  Monoclinic.  Axes 
0.926;  /9=  76°  20'.  Crystals  are  usually 
small  and  flat,  but  sometimes  large.  Fig. 
361  shows  the  pinacoids  a  and  b,  the  unit 
pyramid,  prism  and  dome  /,  m  and  o  and 
the  prism  /=  (20,  :  b  :  coc) ;  { 120}.  Sup- 
plement angles  mm  =  86°  34'  ;  ad  =  39° 

OPTICALLY  -f ,  with  axial  plane  nearly  a 
and  acute  bisectrix  nearly  vertical.  Axial 
angle  in  red  light  2E—  29°  to  31°. 


Sp.  gr.,  4.9-5-3. 
OPAQUE,  to  translucent. 
TENACITY,  brittle. 
CLEAVAGE,  basal,  perfect. 


Physical  Characters.  —  H.,  5-5.5. 

LUSTRE,  resinous. 

STREAK,  white. 

COLOR,  clove  or  reddish  brown, 

yellow. 

BEFORE  BLOWPIPE,  ETC.  Turns  gray  when  heated,  but  does  not 
fuse.  Is  decomposed  by  hydrochloric  acid  with  a  white  residue. 
Solutions  added  to  a  nitric  acid  Solution  of  ammonium  molybdate 
produce  a  yellow  precipitate. 

REMARKS. — Occurs  as  crystals  in  the  pegmatites  of  Norway  and  Sweden,  and  in 
large  crystals  and  masses  at  Amelia  County,  Va.  Disseminated  in  gneiss  in  Brazil 
and  in  North  Carolina  and  as  needles  or  minute  crystals  in  apatite  of  Arendal,  Norway 
Hurdstown,  N.  J.,  and  elsewhere. 

Residual  deposits  occur  in  Brazil  as  sea  shore  sands  near  Prado,  Bahia,  and 
Esperito  Santo,  and  in  beds  of  gravel  in  Minas  Geraes  and  elsewhere.  Also  found 
in  the  gold  and  platinum  washings  of  Siberia,  Colombia  and  in  North  Carolina 
(formerly  important)  and  the  tin  deposits  of  Malay,  Nigeria  and  Nyassaland. 

XENOTIME. 

COMPOSITION — YtPC"4  (VtzOa  54  to  64,  Ce2Os  o  to  n,  ThOz  o  to  3,  ZrC»2  o  to  2 
per  cent.). 

GENERAL  DESCRIPTION. — Soft  yellow,  brown  or  red  crystals,  zircon-like  in  form 
with  easy  prismatic  cleavage. 


MINERALOGY. 


CRYSTALLIZATION. — Tetragonal,  c  =  0.6187.  Common  forms  unit  prism  m. 
unit  pyramid  p,  second  order  prism  a.  Supplement  angle  pp  =  55°  30'. 

PHYSICAL  CHARACTERS  — Opaque.  Lustre,  resinous  to  vitreous.  Color,  yellows, 
browns  and  flesh  red.  Streak,  paler  than  color.  H.,  4  to  5.  Sp.  gr.  4.45  to  4.56. 
Cleavage,  perfect  parallel  m. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  Bluish  green  flame  with  sulphuric  acid. 
Insoluble  in  acids. 

REMARKS. — Occurrence  like  monazite  in  the  Swedish  pegmatites,  and  the  residual 
deposits  of  Brazil  and  North  Carolina.  Also  in  larger  crystals  at  Alexander  Co.,  N.  C. 

ZIRCO  N.— Hyacinth. 

COMPOSITION. — ZrSiO4  (ZrO  67.2,  SiO2  32.8  per  cent.). 

GENERAL  DESCRIPTION. — Small,  sharp  cut,  square  prisms  and 
pyramids  with  adamantine  lustre  and  brown  or  grayish  color. 
Sometimes  in  large  crystals  and  in  irregular  lumps  and  grains. 

CRYSTALLIZATION. — Tetragonal.  Axis  c  =  0.640.  Common 
forms:  unit  prism  m,  unit  pyramid  p,  second  order  prism  a,  and 
pyramids  u  =  (a  :  a  :  3$);  {331}  and  x  =  (a  :  $a  :  3^);  (311). 
Supplement  angles  pp  =  56°  41';  uu  =  83°  9';  mu  =  20°  12'; 
ax  =  31°  53';  mp  =  47°  50';  pp  over  top  84°  20'. 

Optically  +  with  strong  refraction  and  double  refraction  (a  = 
1.9239;  7  =  1.9628  for  yellow  light). 


FIG.  362. 


FIG.  363. 


FIG.  364. 


FIG.  365. 


Physical  Characters.     H.,  7.5.     Sp.  gr.,  4.68  to  4.70. 

LUSTRE,  adamantine.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  brown,  reddish,  gray,  colorless,  green,  yellow. 
CLEAVAGES,  imperfect,  parallel  to  both  pyramid  and  the  prism. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  losing  color  and  sometimes 
becoming  white.     Insoluble  in  acids  or  in  soda. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     315 

REMARKS.— Occurs  in  minute  crystals  in  granite  and  especially  in  nephelite  or 
augite  syenite,  as  in  the  Wichita  Mts.,  Oklahoma.  Larger  crystals  occur  in  pegma- 
tites as  in  Southern  Norway,  Litchfield,  Maine,  and  Canada.  Less  common  in 
crystalline  schists  (Tyrol)  and  occasionally  in  beds  of  iron  ore,  Mineville,  N.  Y., 
and  Fredericksvarn,  Norway. 

Residual  deposits  often  contain  zircon  as  in  the  gold  sands  of  North  Carolina 
and  the  gem  gravels  of  Ceylon  and  Expailly,  France. 

THORITE— Orangite. 

COMPOSITION. — ThSiO4,  carrying  some  water. 

GENERAL  DESCRIPTION. — Black  or  orange-yellow  tetragonal  crystals  like  those  of 
zircon.  Also  found  massive. 

PHYSICAL  CHARACTERS. — Translucent  to  transparent.  Lustre  resinous.  Color 
black,  brown  and  orange.  Streak,  orange  to  brown.  Brittle.  H.,  4.5-5.  Sp.  gr., 
4.4-5.2. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  Gelatinizes  with  hydrochloric  acid  before 
being  heated  by  blowpipe  but  not  after.  In  closed  tube  yields  water  and  the  orange 
variety  becomes  nearly  black  while  hot,  but  changes  to  orange  again  on  cooling. 

REMARKS. — Thorite  occurs  in  large  black  crystals  in  a  pegmatite  near  Arendal, 
Norway,  and  as  masses  and  crystals  of  orange  color  at  Lb'vo  and  other  localities  near 
Brevik,  Norway.  A  mass  was  found  in  the  Champlain  iron  region,  New  York.  It 
occurs  in  veins  in  hornblende  granite  in  Sutherland,  Scotland,  and  at  the  Trotter 
Mine,  New  Jersey. 

CERITE. 

COMPOSITION. — Hydrated  cerium  silicate  with  CeaOs  36  to  72,  Y2Oi  o  to  7,  ZrOt 
o  to  1 1  per  cent. 

GENERAL  DESCRIPTION. — Granular  masses  between  clove  brown  and  cherry  red 
in  color.  Rarely  crystals.  Resembles  red  granular  corundum. 

CRYSTALLIZATION. — Orthorhombic  highly  modified  short  prisms. 

PHYSICAL  CHARACTERS. — Nearly  opaque.  Luster,  dull  to  resinous.  Color, 
cherry  red,  brown,  gray.  Streak,  gray  or  white.  H.,  5.5.  Sp.  gr.,  4.86. 

BEFORE  BLOWPIPE,  ETC. — Infusible..  In  closed  tube  yields  water.  With  soda 
a  yellow  slag  nearly  colorless  on  cooling.  Gelatinizes  with  hydrochloric  acid. 

REMARKS. — Occurs  at  Bastnas,  Sweden,  as  a  bed  in  gneiss  with  allanite,  chalco- 
pyrite,  and  other  minerals. 

GADOLINITE. 

COMPOSITION. — Yt2Be2FeSi2Oio  (Yttrium  Oxides  51.8,  BeO  10.0,  FeO  14.3,  SiO2 
23.9  per  cent.). 

GENERAL  DESCRIPTION. — Rounded  or  nodular  masses,  internally  glassy  and 
nearly  black,  externally  earthy  and  reddish  or  yellow.  Somewhat  resinous  in  luster. 
Sometimes  in  coarse  monoclinic  crystals. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  vitreous  to  greasy.  Color,  black 
or  greenish  black.  Streak,  greenish  gray.  H.,  6.5  to  7.  Sp.  gr.,  4.24  to  4.47. 

BEFORE  BLOWPIPE,  ETC.  Infusible  but  swells  and  cracks  and  if  glassy  glows 
brightly.  Gelatinizes  with  hydrochloric  acid. 

REMARKS. — Occurs  in  pegmatite  veins.  Abundant  at  Baringer  Hill,  Llano  Co., 
Texas.  Found  at  Hittero  and  Riser,  Norway,  and  Kararfvet  and  Ytterby, 
Sweden, 


Lead 

Pb 

Isometric 

Galenite 

PbS 

Isometric 

Bournonite 

PbCuSbSa 

Orthorhombic 

Jamesonite 

Pb2Sb2S5 

Orthorhombic 

Clausthalite 

PbSe 

Isometric 

Minium 

Pb304 

Anglesite 

PbS04 

Orthorhombic 

Pyromorphite 

Pb5Cl(P04)3 

Hexagonal 

Mimetite 

Pb6Cl(AsO4)3 

Hexagonal 

Cerussite 

PbC03 

Orthorhombic 

316  MINERALOGY. 

THORIANITE.  ThO2U3O8  (ThO2  70  to  80,  Ce2O3  12  to  28,  UO3 12  to  25,  ZrO2  up 
to  3  per  cent-),  occurring  as  small  black  water  worn  cubic  crystals  found  in  the  Ceylon 
gem  gravels.  Sp.  gr.,  9.3. 

THE  LEAD  MINERALS. 

The  minerals  described  are: 

Metal 

Sulphide 

Sulphantimonites 

Selenide 

Oxide 

Sulphate 

Phosphate 

Ar  senate 

Carbonate 

Zinkenite,  plagionite,  boulangerite,  geocronite,  linarite  and  phos- 
genite  are  briefly  mentioned.  Other  lead  minerals  described 
elsewhere  are  crocoite,  vanadinite,  descloizite,  wulfenite,  and  lead  is 
found  in  many  other  species. 

ECONOMIC   IMPORTANCE. 

The  world  uses  about  1 ,500,000  tons  of  lead  per  year,  of  which 
this  country,  in  1915,  produced  565,356  tons  from  domestic  ores.* 
Of  this  221,797  tons  was  soft  lead,  mainly  produced  in  Missouri, 
containing  almost  no  silver  and  gold.  During  the  same  year 
317,463  tons  of  lead  was  desilverized;  indeed,  it  may  be  said  that 
by  far  the  most  important  use  of  lead  ore  is  to  mix  and  smelt  with 
silver  ores,  whereby  metallic  lead  containing  silver  and  gold  are 
obtained. 

The  principal  use  of  metallic  lead  is  in  the  manufacture  of  white 
lead  and  large  amounts  are  used  for  the  preparation  of  red  lead, 
litharge,  shot,  lead  pipe  and  sheet  lead.  A  certain  amount  of 
lead  containing  antimony,  24,370  tons  in  1915,  is  produced  which 
is  used  in  type  and  in  alloys  for  friction-bearings. 

The  argentiferous  lead  ores  of  the  west,  which  ordinarily  run 
low  in  lead  are  smelted  in  blast-furnaces.  The  ore,  if  it  contains 
much  sulphur,  is  roasted,  to  remove  the  sulphur  and  other 
volatile  constituents,  and  is  then  fused,  forming  a  silicate,  which  is 

*  Engineering  and  Mining  Journal,  1916,  p.  56. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     317 

charged  in  the  furnace  with  the  proper  proportions  of  fuel  and  flux 
(limestone,  hematite,  etc.).  The  reduction  takes  place  under  the 
action  of  the  blast.  Metallic  lead,  carrying  most  of  the  silver, 
is  produced,  and  if  either  sulphur  or  arsenic  is  present,  a  sulphide 
(matte)  and  an  arsenide  (speiss)  of  iron,  copper,  etc.,  will  form, 
and  above  all  these  will  float  the  slag  composed  of  the  gangue  and 
the  flux. 

The  furnace  is  usually  oblong  in  section,  and  the  hearth  is  con- 
nected, by  a  channel  from  the  bottom,  with  an  outer  basin  or  well, 
so  that  the  metal  stands  at  the  same  level  in  each  and  can  easily 
be  ladled  out.  Above  the  hearth,  and  enclosing  the  smelting  zone, 
are  what  are  called  the  water  jackets,  in  which  cold  water  circu- 
lates. The  furnace  gases  pass  through  a  series  of  condensing 
chambers. 

The  matte,  speiss  and  the  dust  collected  in  the  condensing  cham- 
bers are  all  treated  for  silver,  gold,  lead,  copper,  etc.,  usually  at 
different  works.  The  metallic  lead,  or  base  bullion,  is  desilverized 
by  remelting  in  large  kettles,  raising  it  to  the  melting-point  of  zinc, 
adding  metallic  zinc  and  cooling  to  a  point  between  the  melting- 
points  of  zinc  and  lead.  The  lighter  solidified  zinc  separates,  carry- 
ing with  it  the  silver  and  gold,  and  forms  a  crust  on  the  surface  of 
the  lead,  from  which  it  is  skimmed. 

The  lead  is  further  purified  and  the  zinc,  gold  and  silver  sepa- 
rated electrolytically  or  by  distillation. 

FORMATION   AND    OCCURRENCE    OF   LEAD    DEPOSITS. 

The  evidence  as  to  the  presence  of  lead  minerals  as  primary 
constituents  of  igneous  rocks  is  not  very  conclusive.  Minute 
amounts  have  been  found  in  a  few  analyses.  Lead  forms  no 
important  silicates.*  The  great  lead  deposits  appear  to  be 
galenite  as  a  primary  mineral  deposited  with  other  sulphides 
especially  sphalerite 

No  deposits  due  to  magmatic  segregation  are  known. 
Vein  Deposits. 

These  are  estimated  to  supply  one  third  of  all  the  lead  as  opposed 
to  one  half  in  metasomatic  replacements.*  Veins  are  more  or 

*  Rare  species  barysilite,  hyalotekite,  ganomalite. 
t  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  775. 


318  MINERALOGY, 

less  directly  connected  with  intrusions  of  igneous  rock  and 
may  be  in  crystalline  schists  or  igneous  rocks  or  the  older 
sediments  and  are  often  rich  in  silver.  At  Freiberg,  Saxony, 
they  are  in  gneiss,  at  Clausthal,  Harz;  and  Przibram,  Bohemia; 
in  clay  slate  and  graywacke,  at  Linares,  Spain ;  in  granite.  Other 
important  veins  are  at  Kapnik,  Hungary;  Shoshone,  Idaho; 
Cornwall,  England. 

Replacements.* 

Usually  in  limestone  or  dolomite  as  in  Missouri,  Wisconsin, 
Illinois  and  Kentucky;  Leadville  and  Aspen,  Colorado;  Park 
City  and  Tintic,  Utah ;  Eureka,  Nevada;  Elkhorn,  Mont. ;  Derby- 
shire and  Cumberland,  England;  Raibl  and  Bleiberg,  Carinthia; 
Iglesias,  Sardinia;  Sala,  Sweden;  and  Upper  Silesia. 

Contact  Deposits. 

The  greatest*  lead  mine,  Broken  Hill,  New  South  Wales,  was 
regarded  as  "saddle  lodes, "f  p.  328,  but  is  now  said  to  be  a 
contact  deposit,  the  ores  intergrown  with  garnet,  rhodonite,  etc. 
Other  contact  deposits  are  South  Mountain,  Idaho,  and  Magdalen 
Mines,  New  Mexico. 

LEAD.— Native  Lead. 

COMPOSITION. — Pb,  with  sometimes  a  little  Sb  or  Ag. 

GENERAL  DESCRIPTION. — Usually  small  plates  or  scales  or  globular  masses  em- 
bedded in  other  minerals.  Very  rarely  in  octahedrons  or  dodecahedrons. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre  metallic.  Color  and  streak  lead  gray. 
H.,  1.5.  Sp.  gr.,  11.37.  'Malleable. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily,  coating  charcoal  with  yellow  oxide,  and 
tinging  flame  light  blue.  Soluble  in  dilute  nitric  acid. 

GALENITE.— Galena. 

COMPOSITION. — PbS  (Pb  86.6  per  cent.),  usually  with  some 
silver  and  frequently  sulphide  of  antimony,  bismuth,  cadmium,  etc. 

GENERAL  DESCRIPTION. — A  soft,  heavy,  lead-gray  mineral,  with 
metallic  lustre  and  easy  cubical  cleavage.  Sometimes  in  crystals. 
Rarely  fine-grained  or  fibrous. 

*  Deposited  as  simple  sulphides,  chiefly  galenite  and  sphalerite,  sometimes  with 
pyrite  and  chalcopyrite.     Later  oxidation  and  weathering  forms  carbonate,  sulphate, 
phosphate,  etc. 

*  Said  to  yield  yearly  about  one  ninth  of  world's  production  of  lead.     Beyschlag, 
Vogt  and  Krusch,  p.  1102. 

t  Ibid.,  1173- 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.     319 


CRYSTALLIZATION. — Isometric.  Usually  the  cube,  Fig.  366,  or 
cubo-octahedron,  Fig.  367,  sometimes  octahedral  or  showing  that 
rare  form  the  trisoctahedron  r  =  (a  :  a  :2a);  {221};  Fig.  368. 
Sometimes  twinned  or  in  skeleton  crystals  or  reticulated. 


FIG.  366. 


FIG,  367. 


FIG.  368. 


Physical  Characters. — H.,  2.5.     Sp.  gr.,  7.4  to  7.6. 

LUSTRE,  metallic  OPAQUE. 

STREAK,  lead-gray.  TENACITY,  brittle. 

COLOR,  lead-gray.  CLEAVAGE,  cubic,  very  easy. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  decrepitates  and  fuses 
easily,  yielding  in  O.  F.  a  white  sulphate  coat,  and  in  R.  F.  a  yellow 
coat  and  metallic  button  of  lead.  With  bismuth  flux,  gives  a 
strong  iodide  coat,  which  appears  chrome-yellow  on  plaster  and 
greenish-yellow  on  charcoal.  With  soda,  yields  malleable  lead 
and  a  sulphur  test.  Soluble  in  excess  of  hot  hydrochloric  acid, 
from  which  white  lead  chloride  separates  on  cooling.  Soluble  also 
in  strong  nitric  acid,  with  separation  of  sulphur  and  lead  sulphate. 

SIMILAR  SPECIES. — Characterized  by  its  cleavage,  weight  and 
appearance,  except  in  some  fine-grained  varieties. 

REMARKS. — The  occurrences  have  been  described,  p.  317.  The  great  producing 
states  in  1914  were  Missouri,  192,612;  Idaho,  174,263;  Utah,  85,622;  Colorado, 
37,106  (short  tons  of  lead). 

USES. — It  is  the  chief  ore  of  lead,  and  as  it  usually  contains 
silver,  the  silver-bearing  deposits  are  more  frequently  worked  than 
the  purer  galenite,  and  both  the  lead  and  silver  are  recovered. 

BOURNONITE. 

COMPOSITION. — PbCuSbSa,  (Pb  42.5,  Cu  13.0,  Sb  24.7,  S  19.8  per  cent.). 

GENERAL  DESCRIPTION. — A  gray  metallic  mineral,  nearer  steel-gray  than  galenite, 
and  occurring  fine-grained,  massive  and  in  thick  tabular  crystals,  or  cross  Fig.  370, 
and  "cog-wheel"  twins.  Supplement  angles  mm  =  86°  20',  co  =  43°  43',  cu  =  33° 


320 


MINERALOGY, 


FIG.  369. 


FIG.  370. 


Harz. 


Kapnik. 


PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color,  steel-gray  to  nearly 
black.  Streak,  steel-gray.  H.,  2.5  to  3.  Sp.  gr.,  5.7  to  5.9.  Brittle.  Cleavages 
imperfect. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses  easily,  yielding  heavy  white  sub- 
limate, and  later  a  yellow  sublimate.  With  bismuth  flux  yields  strong  greenish- 
yellow  coat  on  charcoal  and  a  mingling  of  chrome  yellow  and  peach  red  on  plaster. 
After  sublimates  have  formed,  the  residue  will  color 'the  flame  deep  green,  or  if  mois- 
tened with  a  drop  of  hydrochloric  acid,  will  color  the  flame  bright  azure  blue.  Soluble 
in  nitric  acid  to  a  green  solution,  with  formation  of  a  white  insoluble  residue. 

REMARKS. — Occurs  as  secondary  mineral  in  veins  as  at  Kapnik,  Hungary; 
Endellion,  Cornwall;  Reported  in  Yavapai  Co.,  Arizona. 

JAMESONITE.— Feather  Ore. 

COMPOSITION. — Pb2Sb2S5.     (Pb  50.8,  Sb  29.5,  S  19.7  per  cent.). 

GENERAL  DESCRIPTION. — Steel-gray  to  dark-gray  metallic  needle  crystals,  or  hair- 
like  and  felted;  also  compact  and  fibrous  massive. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color,  steel-gray  to  dark- 
lead  gray.  Streak,  grayish-black.  H.,  2  to  3.  Sp.  gr.,  5.5  to  6.  Brittle. 

BEFORE  BLOWPIPE,  ETC. — Decrepitates  and  fuses  very  easily,  and  is  volatilized, 
coating  the  charcoal  white  and  yellow  as  in  bournonite.  With  bismuth  flux,  reacts 
like  bournonite.  In  closed  tube,  yields  dark-red  sublimate,  nearly  black  while  hot. 
Soluble  in  hot  hydrochloric  acid,  with  effervescence  of  hydrogen  sulphide. 

REMARKS. — Secondary  in  veins  with  stibnite  as  at  Freiberg,  Saxony,  and  Sevier 
Co.,  Arkansas;  or  with  galenite  as  at  Przibram.  In  Zimapan,  Mexico,  occurrs  in  com- 
mercial quantity. 


The  following  four  species  are  representative  of  a  series  of  secon- 
dary minerals  formed  in  lead  and  antimony  veins.  In  blowpipe 
characters  all  are  like  jamesonite.  Hardness,  2.5  to  3.5.  The 
specific  gravity,  5.3  to  6.5,  increases  with  the  lead. 

ZINKENITE.— PbS.Sb2S3.  Columnar  and  fibrous  steel-gray  material  from  Wolfs- 
berg,  Harz,  Sevier  Co.,  Ark.,  etc. 

PLAGIONITE. — 5PbS.4Sb2S3.  Druses  of  short  thick  notably  oblique  (monoclinic) 
crystals  of  dark  lead  gray  color  from  Wolf ach,  Baden;  Wolfsberg,  Harz,  etc. 

BOULANGERITE. — 3PbS.Sb2S3.  Feathery  masses  and  needle  crystals'of  bluish 
lead  gray  color,  often  covered  with  yellow  spots  due  to  oxidation. 

From  Echo  District,  Nevada;  Bottino,  Tuscany,  etc. 

GEOCRONITE. — 5PbS.Sb2S3.  Light  lead  gray  massive  granular  material  from 
Sala,  Sweden  and  Inyo  Co.,  Calif. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     321 

CLAUSTHALITE. 

COMPOSITION. — PbSe,  (Pb  72.4,  Se  27.6  per  cent.)-     Many  contain  silver  or  cobalt 

GENERAL  DESCRIPTION. — Bluish  gray  fine  granular  masses  of  metallic  lustre. 
Rarely  foliated.  Resembles  galenite. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color,  bluish  lead  gray. 
Streak,  grayish  black.  H.,  2.5  to  3.  Sp.  gr.,  7.6  to  8.8. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  and  yields  odor  like  decayed  horse- 
radish, coats  the  charcoal  with  a  white  sublimate  with  red  border,  and  later  a  yellow 
coat  forms.  In  open  tube  gives  a  red  sublimate.  With  soda  yields  a  mass  which 
blackens  silver. 

MINIUM. 

COMPOSITION. — Pb  O4.     (Pb  90.6  per  cent.). 

GENERAL  DESCRIPTION. — A  vivid  red  powder  or  loosely  compacted  mass  of  dull  or 
greasy  lustre.  Often  intermixed  with  yellow. 

PHYSICAL  CHARACTERS. — Opaque.  Bright  red.  Lustre,  dull  or  greasy.  Streak, 
orange  yellow.  H.,  2  to  3.  Sp.  gr.,  4.6. 

BEFORE  BLOWPIPE,  ETC. — Is  reduced  to  metallic  lead,  and  yields  the  characteristic 
lead  sublimates. 

REMARKS. — The  artificial  product  is  the  red  lead  of  commerce.  Chiefly  an  altera- 
tion of  galenite  or  cerussite,  sometimes  pseudomorphous  after  them.  Occurs  Wythe 
Co.,  Virginia;  Leadhills,  Scotland;  Bleialf,  Eifel;  Brilon,  Westphalia,  etc. 

ANGLESITE. 

COMPOSITION.— PbS04,  (PbO  73.6,  SO3  264  per  cent.). 

GENERAL  DESCRIPTION. — Simple  crystals,  often  transparent  and 
colorless,  white  brittle  masses  and  compact  granular  masses  of 
gray  color  from  intermixed  galenite.  Sometimes  in  concentric 
layers  around  a  core  of  unaltered  galenite. 

FIG.  371.  FIG.  372. 


Phoenixville,  Pa. 


CRYSTALLIZATION. — Orthorhombic.  Axes  a  :  b  :  c—  0.785  :  i  : 
1.289.  Crystals  vary  greatly  in  type,  but  are  rarely  twinned. 
Unit  prism  m  and  domes  such  as  n  =  (a  :  oo  b  :  Y^c);  {102}  ; 
z  =  (a  :  oo  b  :  %c]\  (104) ;  and  pyramids  q  =  (20,  :b  :  c);  {122} 
are  frequent. 

Supplement  angles:  mm  =  76°  17';  en  =  33°  24';  cz  =  22°  19'; 
cq  =  56°  48'- 


322  MINERAL  OGY. 

Physical  Characters.     H.,  3.     Sp.  gr.,  6.12  to  6.39. 

LUSTRE,  adamantine  to  vitreous.     TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  very  brittle. 

COLOR,  colorless,  white,  gray;  rarely  yellow,  blue  or  green. 

CLEAVAGE,  basal  and  prismatic  (90°  and  103°  43')- 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  decrepitates  and  fuses 
easily  to  a  glassy  globule  pearly  white  on  cooling.  In  R.  F.  is  re- 
duced and  yields  metallic  lead  and  the  yellow  sublimate.  With 
soda  yields  the  sulphar  reaction.  Insoluble  in  hydrochloric  acid 
but  is  converted  into  chloride.  Slowly  soluble  in  nitric  acid. 

SIMILAR  SPECIES, — It  differs  from  the  carbonate,  cerussite,  in 
absence  of  twinned  crystals  and  of  effervescence  in  acids.  It  is 
heavier  than  barite  and  celestite,  and  yields  lead. 

REMARKS. — Anglesite  is  formed  by  the  oxidation  of  galenite  and  found  wherever 
exposed  deposits  of  galenite  occur.  Large  quantities  have  been  found  in  Sierra 
Mojada,  Mexico;  Leadville,  Colorado;  Cerro  Gordo,  California;  Yuma  Co.,  Arizona. 
An  earthy  variety  occurs  near  Coquimbo,  Chili.  Famous  localities  for  crystals  are 
Monte  Poni  Sardinia;  Wheatley's  Mine,  Pennsylvania;  Anglesey,  England  and 
Felsobanya,  Hungary. 

LINARITE.— [(PbCu)OH]2SO4.     In  small,  deep  blue,  monoclinic  crystals. 

PYROMORPHITE. 

COMPOSITION.— Pb5Cl(PO4)3,  (PbO  82.2,  P2O5  15.7,  Cl  2.6  per 
cent.)  often  with  some  As,  Fe  or  Ca. 

GENERAL  DESCRIPTION. — Short  hexagonal  prisms  and  branching 
and  tapering  groups  of  prisms  in  parallel  position.  The  color 
is  most  frequently  green,  brown,  or  gray.  Also  in  moss-like 
interlaced  fibers  and  masses  of  imperfectly  developed  crystals. 
Less  frequently  in  globular  and  reniform  masses. 

CRYSTALLIZATION. — Hexagonal,  class  of  third  order  pyramid, 

P-  57- 

Axis  c  =  0.736.  Usual  form  prism  m  and  base  c.  Faces  m 
horizontally  striated,  sometimes  tapering. 

Physical  Characters.     H.,  3.5  to  4.     Sp.  gr.,  5.9  to  7.1. 

LUSTRE,  resinous.  TRANSLUCENT  to  opaque. 

STREAK,  white  to  pale  yellow.     TENACITY,  brittle. 

COLOR,  green,  gray,  brown;  also  yellow,  orange,  white. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  to  a  globule  which 
on  cooling  does  not  retain  its  globular  form  but  crystallizes,  show- 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.     323 

ing  plane  faces.  In  reducing  flame  yields  white  coat  at  a  distance 
and  yellow  coat  nearer  the  assay,  and  a  brittle  globule  of  lead. 
In  closed  tube  with  magnesium  ribbon  yields  a  phosphide  which, 
moistened  with  water,  evolves  phosphine.  With  salt  of  phos- 
phorus saturated  with  copper  oxide  yields  an  azure  blue  flame. 
Soluble  in  nitric  acid,  and  from  the  solution  ammonium  molybdate 
throws  down  a  yellow  precipitate. 

SIMILAR  SPECIES. — Differs  from  other  lead  minerals  in  fusing 
to  a  crystalline  globule  without  reduction. 

REMARKS. — A  decomposition  product  of  galenite  and  other  lead  minerals  occurring 
near  the  outcrop  and  sometimes  in  sufficient  quantities  to  be  smelted.  Found  at 
Phoenixville,  Pa.,  Davidson  county,  N.  C.,  Lenox,  Me.,  Cour  d'AIene,  Idaho,  and  in 
many  foreign  localities,  notably  Huelgoet,  Brittany;  Ems,  Nassau;  Berezov,  Siberia; 
Cornwall,  Derbyshire  and  Cumberland,  England;  Leadhills,  Scotland. 

MIMETITE.— 3Pb3(AsO4)2  +  PbChsor  Pb6Cl(AsO4)3,  of  ten  with  some  replacement 
by  P  or  Ca. 

Pale  yellow  to  brown  hexagonal  prisms  or  globular  groups  of  crystals.  Sometimes 
incrusting.  Streak,  white.  H.,  3.5.  Sp.  gr.,  7.0  to  7.25,  lower  when  Ca  is  present. 

On  charcoal  fuses  easily  and  is  reduced  to  metallic  lead,  coating  the  coal  with 
white  and  yellow  sublimates  and  yielding  strong  arsenical  odor.  Found  in  Cumber- 
land, England;  Cerro  Gordo,  Calif.;  Yuma  Co.,  Arizona,  etc. 

CERUSSITE.— White  Lead  Ore. 

COMPOSITION.— PbCO3,  (PbO,  83.5 ;  CO2, 16.5  per  cent.).  Often 
carries  silver. 

GENERAL  DESCRIPTION. — Very  brittle,  white  or  colorless  ortho- 
rhombic  crystals;  silky,  milk-white  masses  of  interlaced  fibres; 
granular,  translucent,  gray  masses  and  compact  or  earthy,  opaque 
masses  of  yellow,  brown,  etc.,  colors. 


FIG.  373. 


FIG.  374. 


CRYSTALLIZATION. — Orthorhombic.  Axes  a  :  b  :  c  =  0.610  :  i  : 
0.723.  Common  forms:  unit  pyramid  p,  and  prism  m  and  a  series 
of  brachy  domes  such  as  x  =  («>  a  :  b  :  %€);  {012} ;  w  =  (<*>  a  : 


324  MINERALOGY. 

b  :  2c);  {021}  andv  =  (oo  a  :  b  :  y);  {031}.  Frequently  twinned 
about  m  sometimes  yielding  six-rayed  groups  as  in  Fig.  374. 
Supplement  angles  are  mm  =  62°  46',  pp  =  50°,  ww  =  110°  40'. 

Physical  Characters. — H.,  3  to  3.5.     Sp.  gr.,  6.46  to  6.51. 

LUSTRE,  adamantine,  silky.          TRANSPARENT  or  translucent. 

STREAK,  white.  TENACITY,  very  brittle. 

COLOR,  white,  gray,  colorless  or  colored  by  impurities. 

CLEAVAGES,  parallel  to  prism  and  brachy  dome. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  decrepitates,  fuses  and 
gives  a  yellow  coating,  and  finally  a  metallic  globule.  In  closed 
tube,  turns  yellow,  then  dark,  and  on  cooling  is  yellow.  Effer- 
vesces in  acids,  but  with  hydrochloric  or  sulphuric  acid  leaves  a 
white  residue. 

SIMILAR  SPECIES. — Distinguished  from  anglesite  by  efferves- 
cence in  acids  and  by  frequent  occurrence  of  twinned  crystals. 
Has  higher  specific  gravity  than  most  carbonates. 

REMARKS. — Found  in  the  oxidized  zone  of  lead  deposits.  Formerly  the  principal 
mineral  of  the  Leadville,  Colorado  deposits  and  in  large  masses  in  Pima  Co.,  Arizona. 
Now  abundant  at  Cour  d'Alene,  Idaho;  Cerro  Gordo,  California,  and  especially 
Broken  Hill,  New  South  Wales. 

PHOSGENITE. — Pb2Cl2CO3.  In  transparent,  colorless  or  gray  tetragonal 
crystals. 

THE   BISMUTH   MINERALS. 

The  minerals  described  are: 


Metal 

Bismuth 

Bi 

Hexagonal 

Sulphide 

Bismuthinite 

Bi2S3 

Orthorhombic 

Tetturide 

Telradymite 

Bi2(Te.S)8 

Hexagonal 

Carbonate 

Bismutite 

(BiO)2CO3.H2O 

Oxide 

Bismite 

Bi203 

Orthorhombic 

Bismuth  is  the  metallic  element  in  other  species  such  as  pucherite, 
eulytite,  cheleutite,  and  aikinite,  and  a  constituent  of  a  series  of 
so-called  sulpho-bismutites.* 

ECONOMIC   IMPORTANCE. 

The  important  ores  are  bismuthinite,  bismuth  and  bismite.  The 
world's  supply  comes  chiefly  from  Bolivia,  the  principal  company 
producing  437  tons  in  1914  and  this  country  following  with  no, 
tons  obtained  entirely  as  a  by-product  in  electrolytic  lead  refining, 

*  Such  as  chiviatite,  cuprobismutite,  emplectite,  matildite  and  klaprotholite. 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.     325 

largely  from  unidentified  species,  and  Peru  and  Australia  supplying 
the  rest. 

The  uses  of  bismuth  are  chiefly  dependent  upon  its  property  of 
forming  easily  fusible  alloys  with  other  metals,  especially  tin,  lead, 
and  cadmium.  These  alloys  expand  in  cooling,  and  are  therefore 
used  in  type  metal,  in  reproducing  woodcuts,  in  making  safety 
plugs  for  boilers,  etc.  Also  in  anti-friction  metals  and  pewter. 
The  salts  of  bismuth  have  numerous  uses  in  medicine  and  in  the 
arts,  are  used  in  calico  printing,  cosmetics,  as  pigments,  in 
making  glass  of  high  refractive  po\ver,  and  to  impart  lustre  to 
porcelain. 

In  Saxony  the  ores  are  first  roasted  to  free  them  from  sulphur r 
arsenic  and  other  volatile  constituents.  After  roasting  they  are 
smelted  in  crucibles  with  iron,  charcoal  and  slag,  the  melted  bismuth 
settling  out  in  the  bottom  of  the  crucible ;  or  the  roasted  ores  may 
be  treated  with  strong  hydrochloric  acid  (i  :  i)  which  dissolves  the 
bismuth  and  from  which  it  is  precipitated  as  oxychloride  by  the 
addition  of  water.  The  metal  may  be  further  purified  electro- 
lytically.  When  bismuth  is  found  to  be  present  in  the  cupellation 
of  lead  ore,  it  is  recovered  by  saving  the  last  products  of  oxidation. 
From  this  by  solution  in  hot  hydrochloric  acid  and  precipitation 
as  oxychloride  the  bismuth  may  be  recovered.  More  recentlyf 
the  cupellation  slag  is  fused  with  sodium  sulphate  and  carbon  at 
about  1500°  C.  giving  three  layers  bismuth,  copper  matte,  and 
soda  slag. 

FORMATION   AND    OCCURRENCE    OF  BISMUTH  DEPOSITS. 

Veins. 

The  usual  occurrence  is  in  veins  as    in    the    cobalt  bismuth 
veins  at  Schneeberg,  Saxony,  the  silver  cobalt  veins  of  Joachims- 
thai,  Bohemia*  the  tin  silver  veins  of  Bolivia,  and  various  gold 
veins. 
Pegmatites. 

Bismuth  in  quantity  may  also  occur  in  pegmatites  as  in  New 
South  Wales. 

*  Eng.  &  Min.  Journ.  1916,  p.  82. 
f  Mineral  Resources  U.  S.,  1914. 
%  U.  S.  Patent  1,098,854. 


326  MINERALOGY. 

BISMUTH.— Native  Bismuth. 

COMPOSITION. — Bi,  often  alloyed  with  As  or  impure  from  S  or  Te. 

GENERAL  DESCRIPTION. — A  brittle  silver-white  mineral  with  a 
reddish  tinge,  often  in  branching  shapes  or  in  isolated  grains  or 
cleavable  masses. 

Physical  Characters.     H.,  2  to  2.5.     Sp.  gr.,  9.7  to  9.83. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  silver  white.  TENACITY,  sectile  to  brittle. 

COLOR,  reddish  silver  white. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  easily  and  vola- 
tilizes completely,  coating  the  charcoal  with  a  yellow  sublimate. 
With  bismuth  flux  forms  a  chocolate  brown  and  red  coating  which 
is  best  seen  on  plaster,  and  which  is  changed  by  action  of  ammonia 
fumes  to  red  and  orange.  Sojuble  in  strong  nitric  acid  from  which 
solution  water  will  precipitate  a  white  basic  salt. 

SIMILAR  SPECIES. — Bismuth  is  characterized  by  its  silver  streak, 
reddish  tinge,  and  arborescent  structure. 

REMARKS. — Bismuth  in  economic  quantity  is  found  in  the  tin  silver  veins  of  Tasna 
.and  Chorolque,  Bolivia,  in  a  gold-bearing  magnetite  in  Queensland,  Australia,  in  a 
pegmatite  in  New  England  district,  New  South  Wales  and  in  the  silver,  cobalt  and 
tin  veins  of  Saxony  and  Bohemia.  The  metal  is  not  found  in  any  quantity  in  the 
United  States,  although  obtained  at  Monroe,  Conn.,  Colorado,  in  Inyo  Co.,  California, 
.and  in  Chesterfield  district,  South  Carolina. 

BISMUTHINITE. 

COMPOSITION. — Bi2S8,  (Bi  81.2,  S  18.8  per  cent.).     May  contain  Cu  or  Fe. 

GENERAL  DESCRIPTION. — A  lead  gray  mineral  of  metallic  lustre  usually  occurring 
in  foliated  or  cleavable  masses,  or  in  groups  of  long  needle-like  orthorhombic  crystals. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color,  lead  gray  or  lighter, 
often  with  yellow  tarnish.  Streak,  lead  gray.  H.,  2.  Sp.  gr.,  6.4  to  6.5.  Slightly 
sectile. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  yields  some  sulphur,  fuses  easily  with 
spirting,  and  coats  the  coal  with  white  and  yellow  sublimates.  Yfelds  the  character- 
istic bismuth  reactions  with  bismuth  flux  and  with  nitric  acid  as  described  under 
bismuth.  With  soda  gives  sulphur  reaction. 

REMARKS. — Bismuthinite  occurs  in  the  tin  veins  of  Bolivia  and  Cornwall,  in  a 
pegmatite  in  New  England  district,  New  South  Wales,  in  hornstone  at  Wolfach, 
Baden,  and  in  Meymac,  France.  In  this  country  at  Beaver  Co.,  Utah,  and  Inyo 
Co.,  California. 

TETRADYMITE. 

COMPOSITION. — Bi2(Te.S)s  or  BiTeS.     Either  an  alloy  or  a  telluride  of  bismuth. 

GENERAL  DESCRIPTION. — Very  soft,  flexible,  foliated  masses  of  steel-gray  color 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.     327 

and  bright  metallic  lustre,  or  small  indistinct  rhombohedral  crystals.  Will  mark 
paper  like  graphite. 

PHYSICAL  CHARACTERS,  ETC. — Opaque.  Lustre,  metallic.  Color,  pale  steel- 
gray.  Streak,  gray.  H.,  1.5  to  2.  Sp.  gr.,  7.2  to  7.6.  Flexible  in  laminae.  Cleav- 
age, basal. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  easily  and  is  completely  volatilized, 
yielding  a  white  fusible  sublimate,  followed  by  a  yellow  sublimate.  The  flame  during 
fusion  is  colored  blue.  The  white  sublimate  if  placed  on  porcelain  and  moistened 
with  concentrated  sulphuric  acid  becomes  rose  colored.  If  dropped  into  boiling 
concentrated  sulphuric  acid  a  deep  violet  color  is  produced. 

REMARKS. — Occurs  especially  in  gold  veins  or  with  gold  as  at  Schubkau,  Hungary"; 
Orawitza,  Banat;  Tellemark,  Norway,  and  in  this  country  in  Virginia,  North  and 
South  Carolina,  Georgia  and  Montana.  In  quartz  with  gold  in  Arizona. 

BISMUTITE. 

COMPOSITION. — (BiO^COs,  HzO,  variable. 

GENERAL  DESCRIPTION. — A  light  colored  incrustation  or  earthy  mass  or  powder. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  dull  or  vitreous.  Color,  white,  green 
and  yellow.  Streak,  colorless  to  greenish.  H.,  4-4.5.  Sp.  gr.,  6.9-7.7.  Tenacity, 
brittle. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  on  charcoal,  giving  a  yellow  coat  and  in 
R.  F.  a  metallic  globule  which  completely  volatilizes.  With  bismuth  flux  on  plaster 
gives  brown  and  red  coat.  Yields  water  in  closed  tube  and  decrepitates.  Soluble 
with  effervescence  in  strong  HC1,  and  on  dilution  with  much  water  the  white  oxy- 
chloride  of  bismuth  is  precipitated. 

REMARKS. — It  is  usually  associated  with  metallic  bismuth  or  the  sulphide  and 
occurs  at  Brewer's  Mine,  S.  C.,  Phcenix,  Arizona,  Inyo  Co.,  Calif. 

BISMITE.— Bismuth  Ochre. 

COMPOSITION. — Bi2Oa,  Bi  89.6  per  cent,  when  pure. 

GENERAL  DESCRIPTION. — A  yellowish  or  gray  powder  or  earthy  mass. 

PHYSICAL  CHARACTERS. — Opaque.  Color,  grayish,  greenish  or  yellowish  white. 
Lustre,  dull. 

BEFORE  BLOWPIPE,  ETC. — As  for  bismutite  but  does  not  effervesce  with  acids  nor 
yield  water  in  closed  tube. 

REMARKS. — The  400  ft  thick  "gossan"  of  the  Schneeberg  mines  contains  much 
bismite.  It  forms  part  of  the  bismuth  at  Bamford,  Australia,  and  several  mines  in 
Colorado  but  in  general  is  only  a  coating  on  other  bismuth  species. 

THE   ARSENIC   MINERALS. 

The  minerals  described  are: 


Metal 

Arsenic 

As 

Hexagonal 

Sulphides 

Orpiment 

As2S3 

Orthorhombic 

Realgar 

As2S2 

Monoclinic 

Sulpharsenide 

Arsenopyrite 

FeAsS 

Orthorhombic 

Arsenide 

Lollingile 

FeAS2 

** 

Other  species  in  which  arsenic  is  an  essential  constituent  are: 


328  MINERALOGY. 

niccolite,   mimetite,   olivenite,  smaltite,  enargite,  proustite,  cobaltite, 
tennantite,  and  sperrylite. 

ECONOMIC   IMPORTANCE. 

A  rsenopyrite  and  lollingite  are  sometimes  mined  for  their  arsenic 
but  to  a  very  great  extent  arsenic  is  obtained  as  a  by-product  in 
the  roasting  of  ores  of  other  elements  such  as  the  cobalt  ores  of 
Ontario  and  certain  copper,  silver  and  tin  ores. 

The  world's  production  of  "white  arsenic,"  As2O3,  is  possibly 
100,000  metric  tons,f  France  being  the  great  producer  and  Ger- 
many and  this  country  following.  In  1914  this  country  produced 
4,670  short  tonsj  and  imported  1,600. 

Metallic  arsenic  is  ordinarily  produced  by  sublimation  from  a 
mixture  of  the  oxide  and  charcoal,  but  may  be  produced  by  sub- 
limation at  a  high  heat  directly  from  arsenopyrite  out  of  contact 
with  air.  It  is  a  constituent  of  some  useful  alloys,  shot  metal 
being  the  chief. 

The  poisonous  oxide  commonly  known  as  arsenic  or  white 
arsenic,  is  produced  in  large  quantities  by  the  roasting  of  arseno- 
pyrite and  other  arsenical  ores  and  as  a  by-product  in  the  prepara- 
tion of  tin,  silver,  nickel  and  copper.  It  is  used  in  dyeing,  in 
medicine,  in  sheep  washing,  in  calico  printing,  as  a  preservative 
for  timber  and  for  natural  history  specimens,  in  the  manufacture 
of  fly  paper,  and  rat  poisons,  and  in  glass  manufacture.  Many 
important  coloring  matters  as  well  as  the  artificial  red  and  yellow 
sulphides  are  commercial  products.  Paris  green  is  an  arsenate 
of  copper  extensively  used  as  an  insecticide. 

FORMATION  AND  OCCURRENCE  OF  ARSENIC  DEPOSITS. 
There  are  no  known§  metasomatic  replacements  of  arsenopyrite 
or  other  arsenic  minerals. 

Veins. 

(Arsenopyrite,  lollingite  orpiment,  realgar.}  Arsenopyrite  as  at 
the  Devon  Great  Consol.  Mine,  and  carrying  gold  as  in  the  Saddle 

*  Others  are  gersdorffite,  rammelsbergite,  skutterudite. 

t  Statistics  (incomplete)  1912  gives  total  of  94,699  metric  tons,  of  which  France 
produced  81,880.     Mineral  Industry,  1915,  p.  50. 
%  Mineral  Resources  U.  S.,  1914. 
§  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  923. 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.      329 

lodes  of  Bendigo,  West  Australia,  and  Deloro,  Canada.     Realgar 
and  orpiment  as  at  Kapnik,  Hungary. 

Contacts. 

The  gold-bearing  loltingite  and  arsenopyrite  of  Riechenstein, 
Silesia,  occur  as  irregular  lenses  in  highly  altered  tourmaline-bear- 
ing schists,  the  lollingite  intergrown  with  contact  minerals  such  as 
diopside,  vesuvianite,  titanite,  fluorite. 

Orpiment  and  realgar  are  also  stated*  to  occur  in  contacts. 

ARSENIC. — Native  Arsenic. 

COMPOSITION. — As,  generally  with  some  Sb  and  sometimes  with  Bi  or  a  little  Co, 
Ni,  Fe,  Ag  or  Au. 

GENERAL  DESCRIPTION. — A  tin-white  metal,  tarnishing  almost  black.  Usually 
granular,  massive,  with  reniform  surfaces.  Can  frequently  be  separated  in  concentric 
layers.  Rarely  found  in  needle-like  crystals. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  nearly  metallic.  Color,  tin  white, 
tarnishing  nearly  black.  Streak,  tin  white.  H.,  3.5.  Sp.  gr.,  5.63  to  5.73.  Brittle. 
Granular  fracture. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  volatilizes  without  fusion,  yielding  strong 
garlic  odor,  white  fumes,  crystalline  white  sublimate  and  pale  blue  flame.  May  leave 
a  residue  of  impurities. 

REMARKS. — Principally  as  a  minor  constituent  of  silver  or  cobalt-nickel  veins 
as  in  many  mines  in  Saxony,  Bohemia  and  the  Harz,  the  silver  veins  of  Kongsberg, 
Norway;  Chanarcillo,  Chili;  and  Hidalgo,  Mexico.  It  was  found  also  in  pockets  in 
dolomitic  limestone  in  Santa  Cruz  Co.,  Arizona;  and  in  a  vein  in  a  quarry  near 
Montreal. 

REALGAR. 

COMPOSITION. — As2S2,  (As,  70.1;  S,  29.9  per  cent.). 

GENERAL  DESCRIPTION. — A  soft,  orange-red  mineral,  of  resinous 
lustre,  usually  occurring  in  translucent,  granular  masses,  but  also 
compact  and  in  transparent  monoclinic  crystals. 
Physical  Characters.     H.,  1.5  to  2.     Sp.  gr.,  3.4  to  3.6. 

LUSTRE,  resinous.  TRANSLUCENT  to  transparent. 

STREAK,  orange  red.  TENACITY,  slightly  sectile. 

COLOR,  aarora  red,  becoming  orange  yellow  on  long  exposure. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses  easily,  barns  with 
a  blue  flame,  yields  white  fumes,  with  garlic  odor  and  also  odor 
of  sulphur  dioxide  and  is  volatilized  completely.  In  closed  tube 
yields  red  sublimate.  Soluble  in  nitric  acid,  with  separation  of 
sulphur.  Soluble  also  in  potassium  hydroxide  from  which  hy- 
drochloric acid  precipitates  yellow  flakes. 

*'ibid.t  in. 


330 


MINERALOGY. 


REMARKS. — Occurs  with  orpiment  and  sometimes  with  cinnabar  as  a  deposit  from 
hot  springs,  as  in  the  Yellowstone,  also  in  ore  veins  as  at  Kapnik,  Hungary,  and 
Schneeberg,  Saxony. 

ORPIMENT. 

COMPOSITION.— As2S3,  (As,  61;  S,  39  per  cent.). 

GENERAL  DESCRIPTION. — Lemon-yellow,  foliated  masses,  which 
cleave  into  thin,  pearly,  flexible  scales,  and  also  granular  masses 
like  yolk  of  hard-boiled  eggs.  Less  frequently  as  reniform  crusts 
and  imperfect  orthorhombic  crystals. 

Physical  Characters.     H.,  1.5  to  2.     Sp.  gr.,  3.4  to  3.6. 

LUSTRE,  resinous  or  pearly.     TRANSLUCENT  to  nearly  opaque. 

STREAK,  lemon  yellow.  TENACITY,  slightly  sectile. 

COLOR,  lemon  yellow.  CLEAVAGE,  in  plates  or  leaves. 

BEFORE  BLOWPIPE,  ETC. — As  for  realgar,  except  that  the  sub- 
limate in  closed  tube  is  yellow. 

REMARKS. — Often  formed  by  alteration  of  realgar  in  air  and  sunlight  and  found 
with  it  both  in  ore  veins  as  at  Kapnik  and  Felsobanya,  Hungary,  and  in  clay  as  at 
Tajowa,  Hungary,  and  Tooele  and  Iron  Counties,  Utah.  Also  a  sublimation  product 
near  Naples  or  deposited  from  hot  water  as  at  Steamboat  Springs,  Nevada.  Other 
occurrences  are  in  brown  coal  in  Styria,  in  gypsum  in  Hall,  Tyrol.  Foliated  masses 
occur  at  Moldawa,  Banat. 

ARSENOPYRITE.— Mispickel. 

COMPOSITION. — FeAsS.  (Fe  344,  As  46.0,  S  19.6  per  cent.) 
sometimes  with  replacement  of  iron  by  cobalt,  or  arsenic  by  anti- 
mony in  part. 

GENERAL  DESCRIPTION. — Silver  white  to  gray  mineral  with 
metallic  lustre.  Usually  compact  or  in  granular  masses  or  dis- 
seminated grains.  Less  frequently  in  orthorhombic  crystals  or 
columnar. 

CRYSTALLIZATION. — Orthorhombic  a  :  b  :  c  =  0.677  :  J  •'  1.188. 
Common  forms,  unit  prism  m  combined  with  a  brachy  dome 
either  d  =  (cod:  b:  c}\  {on}  or e  =  (cod:  b:  Jc);  (014).  Crossed 
twins,  Fig.  377,  occur  and  fivelings,  as  in  Fig.  197  of  marcasite. 

Supplement  angles  mm  =  68°  13',  dd  =  99°  50',  ee  =  33°  05'. 
Physical  Characters.  H.,  5.5  to  6.  Sp.  gr.,  6  to  6.2. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  grayish-black.  TENACITY,  brittle. 

COLOR,  silver  white  to  steel  gray. 


MINERALS    OF  METALLIFEROUS   ORE  DEPOSITS.     331 


BEFORE  BLOWPIPE,  ETC.— Strikes  fire  with  steel  and  yields  an 
odor  like  that  of  garlic.  In  closed  tube  a  red  sublimate,  yellow 
when  cold,  on  longer  treatment  a  black  sublimate.  On  charcoal 
yields  abundant  white  fumes  and  arsenical  odor  and  coating  and 
fuses  to  a  magnetic  globule.  After  short  treatment  the  residue  is 


FIG.  375. 


FIG.  376. 


FIG.  377. 


soluble  in  hydrochloric  acid  with  evolution  of  hydrogen  sulphide 
and  precipitation  of  the  yellow  sulphide  of  arsenic.  The  residue 
may  react  for  cobalt.  Insoluble  in  hydrochloric  acid.  Soluble 
in  nitric  acid  with  separation  of  sulphur. 

SIMILAR  SPECIES. — Massive  varieties  of  the  metallic  cobalt  min- 
erals and  varieties  of  leucopyrite  resemble  arsenopyrite  but  are 
safely  distinguished  by  blowpipe  tests,  especially  the  closed  tube 
test. 

REMARKS. — Arsenopyrite  is  found  chiefly  in  crystalline  schists  and  the  veins 
which  penetrate  them  associated  with  ores  of  silver,  cobalt,  tin,  zinc,  etc.  Frequently 
gold-bearing  and  worked  as  gold  ore  as  at  Deloro,  Canada;  Passagem,  Brazil;  and 
localities  in  New  South  Wales.  Sometimes  carries  cobalt  (New  England)  or  nickel 
(Bolivia)  and  sometimes  is  in  quantity  sufficient  to  be  mined  for  its  arsenic  (Great 
Consols  Mine,  Devonshire). 

LOLLINGITE.— Leucopyrite. 

COMPOSITION. — Fe3As4  to  FeAs2  sometimes  with  Co,  Ni,  Au  or  S. 

GENERAL  DESCRIPTION. — Massive  silver-white  or  gray  metallic  mineral  some- 
times occurring  in  orthorhombic  crystals,  closely  agreeing  in  angles  with  crystals  of 
arsenopyrite. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color,  silver-white  or  gray. 
Streak,  grayish-black.  H.,  5  to  5.5.  Sp  gr.,  7  to  7.4.  Brittle.  Cleavage,  basal 

BEFORE  BLOWPIPE,  ETC. — Like  arsenopyrite,  except  that  sulphur  reactions  are 
less  pronounced  or  do  not  appear  at  all. 

REMARKS. — Lollingite  is  the  principal  mineral  at  Reichenstein,  Silesia,  and  is 
mined  for  its  arsenic. 


332  MINERALOG  Y. 

THE   ANTIMONY  MINERALS. 

The  minerals  described  are: 

Metal  Antimony  Sb  Hexagonal 

Sulphides  Stibnite  Sb2S3  Orthorhombic 

Kermesite  Sb2S2O  Monoclinic 

Oxides  Valentinite  SbzOs  Orthorhombic 

Senarmontite  SbaOs  Isometric 

Antimony  Ochre  Sb2O4  +  wH2O 

Other  species  containing  antimony  are  numerous,  especially 
compounds  with  lead  and  sulphur.  Species  described  elsewhere* 
are  jamesonite,  bournonite,  tetrahedrite,  livingstonite,  pyrargyrite, 
stephanite,  dyscrasite. 

ECONOMIC   IMPORTANCE. 

The  world  production  of  metallic  antimony  is  about  25,000 
tons  per  year,  principally f  from  China  and  France.  In  addition 
to  this  there  is  a  considerable  production  of  antimonial  lead. 

In  1914  no  metallic  antimony  was  produced  directly  in  this 
country  but  2,705  tons  either  in  antimonial  lead  or  as  a  by- 
product in  refining  copper.  In  1915!  owing  to  increased  demands 
some  smelters  were  working  on  ore  from  Alaska,  Mexico  and 
California. 

The  principal  use  of  antimony  is  in  hardening  alloys  of  lead,  etc., 
such  as  type  metal,  pewter  and  babbitt  metal.  Both  the  metal 
and  the  oxide  are  used  in  making  flint  glass.  The  sulphide  is 
used  in  vulcanizing  rubber,  and  in  safety  matches,  percussion  caps 
and  fireworks,  and  there  are  numerous  uses  for  different  salts  such 
as  "tartar  emetic"  in  medicine  and  others  in  pigments  and  dyes. 

In  smelting,  the  ore  is  heated  and  the  melted  sulphide  drained 
off.  The  sulphide  may  then  be  roasted,  forming  the  oxide,  which 
is  easily  reduced  by  fusion  with  charcoal,  or  more  frequently  the 
sulphide  is  mixed  with  wrought-iron  scraps  and  salt,  placed  in  a 
crucible  or  furnace  and  fused.  The  iron  combines  with  the  sulphur 
and  the  metallic  antimony  settles  to  the  bottom. 

In  a  later  method  the  sulphide  ore  and  oxy sulphide  residue 

*  Others  are  volgerite,  guejarite,  berthierite,  nadorite,  etc. 

t  In  1910,  20,536  metric  tons  of  which  China  produced  13,032,  France  6,390, 
Hungary  1,038.     Mineral  Industry,  1914,  p.  47. 
t  Engineering  and  Mining  Journal,  1916,  p.  79. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.      333 

from  a  former  operation  are  treated  by  a  blast  of  air  in  a  converter. 
The  sulphide  becomes  volatile  oxysulphide  and  is  carried  off  and 
condensed.  Some  metallic  antimony  is  tapped  and  the  oxysul- 
phide is  subsequently  distilled  with  a  reducing  agent. 

THE   FORMATION   AND    OCCURRENCE    OF   ANTIMONY    DEPOSITS. 

There  are  no  great  antimony  deposits.*  Most  frequently  the 
occurrence  is  in  narrow  veins  of  little  depth  in  or  near  eruptive 
rocks  and  there  are  a  few  metasomatic  replacements  and  some 
beds  of  disputed  origin. 

The  usual  primary  mineral  is  stibnite  which  may  be  auriferous 
and  the  usual  oxidized  product  antimony  ochre,   though  in  the 
Algerian  deposits  senarmontite  and  valentinite  predominate. 
Veins. 

In  central  France  are  many  narrow  veins  of  stibnite  which  some- 
times widen  into  lenses,  as  at  Freycenet,  Puy  de  Dome;  La  Lin- 
coulne  is  a  prominent  locality.  The  veins  are  in  granite,  gneiss, 
mica  schist,  graywacke,  etc. 

The  veins  of  lyo  and  Sujo,  Japan,  are  in  schists  and  sometimes 
in  sediments  near  contacts  with  quartz  porphyry. 

Replacements. 

At  Allkhar,  Macedonia,  a  body  of  solid  stibnite  without  gangue 
replaces  dolomite.  Near  the  surface  it  is  antimony  ochre. 

The  beds  of  senarmontite  with  a  little  stibnite  and  some  zinc  and 
lead  minerals  at  Djebel-Hamimat  and  Sidi  Rgheiss,  Algeria;  are 
conformable  to  the  containing  beds  of  limestone  and  marl  and  have 
been  called  sedimentary  but  are  thought  to  be  replacements. f 
Ore  Beds. 

Stibnite  with  jamesonite,  zinkenite,  etc.,  occurs  in  Sevier  Co., 
Arkansas,  in  lenticular  masses  in  sandstone  and  marl. 

ANTIMONY.— Native  Antimony. 

COMPOSITION — Sb,  sometimes  with  As,  Fe  or  Ag. 

GENERAL  DESCRIPTION. — A  very  brittle,  tin-white  metal,  usually  massive,  with 
fine,  granular,  steel-like  texture  or  lamellar  or  radiated.  Very  rarely  in  rhombohedral 
crystals  or  complex  groups. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color,  tin  white.  Streak 
tin  white.  H.,  3  to  3.5.  Sp.  gr.,  6.5  to  6.72.  Very  brittle. 

*  Beyschlag,  Vogt  and  Krusch  (Truscott),  777. 
t  Ibid.,  1190. 


334  MINERAL  OGY. 

BEFORE  BLOWPIPE,  ETC. — Fuses  very  easily,  colors  the  flame  pale  green,  gives 
copious  white  fumes,  which  continue  to  form  as  a  thick  cloud  after  cessation  of  blast, 
and  often  yield  a  crust  of  needle-like  crystals. 

REMARKS. — Antimony  to  the  amount  of  at  least  a  ton  was  found  in  a  quartz 
stibnite  vein  in  argillite  slate  in  Prince  William,  New  Brunswick.  Small  amounts 
occur  in  Kern  Co.,  California,  and  in  Andreasberg,  Harz;  Allemont,  France;  Huasco, 
Chili;  Sarawak,  Borneo,  and  other  localities.  • 

STIBNITE.— Gray  Antimony. 

COMPOSITION. — Sb2S3,  (Sb  71.8,  S  28.2  per  cent.).  Sometimes 
contains  silver  or  gold. 

GENERAL  DESCRIPTION. — A  lead-gray  mineral  of  bright  metallic 
lustre,  occurring  in  imperfectly  crystallized  masses,  with  columnar 
or  bladed  structure;  less  frequently  in  distinct,  prismatic,  ortho- 
rhombic  crystals  or  confusedly  interlaced  bunches  of  needle-like 
crystals;  also  in  granular  to  compact  masses. 

CRYSTALLIZATION. — Orthorhombic.  Axes  a  :  b  :  c  =  0.993  :  i  : 
1.018.  Prismatic  forms,  often  bent  and  curved  or  in  divergent 
groups.  The  vertical  planes  are  striated  longitudinally. 

Common  forms:  unit  prism  m,  unit  pyramid  p  and  pyramid 
s  =  (a  :  b  :  %c)\  {113}.  Supplement  angles  mm  =  89°  34';  pp 
=  70°  48';  55  =  35°  36'. 

Physical  Characters.     H.,  2.     Sp.  gr.,  4.52  to  4.62. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  lead  gray.  TENACITY,  brittle  to  sectile. 

COLOR,  lead  gray,  often  with  black  or  iridescent  tarnish. 

CLEAVAGE,  easy,  parallel  to  brachy  pinacoid,  yielding  slightly 
flexible,  blade-like  strips. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses  very  easily,  yield- 
ing the  same  dense  sublimate  as  antimony.  The  odor  of  sulphur 
dioxide  may  also  be  noticed.  On  charcoal,  with  soda,  yields 
sulphur  test.  In  closed  tube  fuses  easily,  yields  a  little  sulphur 
and  a  dark  sublimate  which  is  brownish  red  when  cold. 

Soluble  completely  in  strong  boiling  hydrochloric  acid,  with  evo- 
lution of  H2S,  with  precipitation  of  white  basic  salt  on  addition  of 
water  and  after  dilution  an  orange  precipitate  on  addition  of 
H2S.  Strong  nitric  acid  decomposes  stibnite  into  white  Sb2O5  and 
S{  Strong  hot  solution  of  KOH  colors  stibnite  yellow  and  partially 
dissolves  it.  From  the  solution  hydrochloric  acid  will  throw  down 
an  orange  precipitate. 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.      335 

SIMILAR  SPECIES. — Differs  from  galenite  in  cleavage,  and  from 
all  sulphides  by  ease  of  fusion  and  cloud-like  fumes. 

REMARKS. — Occurs  as  described  p.  333,  in  narrow  veins  and  as  irregular  replace- 
ments in  limestone  and  in  beds  of  disputed  origin.  The  most  important  localities 
are  Hunan,  China,  and  the  central  plateau  of  France.  Others  are  Queratero,  Mexico; 
lyo  and  Sujo,  Japan;  Borneo;  Pereta,  Tuscany.  In  this  country  it  was  mined  in 
Arkansas  and  is  obtained  from  Alaska  and  California. 

KERMESITE.— Red  Antimony. 

COMPOSITION.— Sb2S2O  or  2Sb2S3-Sb2O3,     (Sb  75.0,  S  20.0,  O  5.0  per  cent.). 

GENERAL  DESCRIPTION. — Fine  hair-like  tufts  of  radiating  fibers  and  needle-like 
crystals,  of  a  deep  cherry-red  color  and  almost  metallic  lustre. 

PHYSICAL  CHARACTERS. — Nearly  opaque.  Lustre,  adamantine.  Color,  dark  cherry 
red.  Streak,  brownish  red.  H.,  I  to  1.5.  Sp.  gr.,  4.5  to  4.6.  Sectile  and  in  thin 
leaves  slightly  flexible. 

BEFORE  BLOWPIPE,  ETC. — As  for  stibnite. 

REMARKS. — Kermesite  results  from  partial  oxidation  of  stibnite.  Extensive  de- 
posits exist  at  Pereta,  Tuscany. 

VALENTINITE. 

COMPOSITION.  — Sb2O3,  (Sb,  83.3  per  cent.). 

GENERAL  DESCRIPTION.  —  Small  white  flat  crystals  ( orthorhombic )  or  radiating 
groups  of  silky  lustre  and  white  or  gray  color.  Also  in  spheroidal  masses  with  radiated 
lamellar  structure. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  adamantine  or  silky.  Color,  white, 
gray,  pale  red.  Streak,  white.  H.,  2.5  to  3.  Sp.  gr.,  5.57. 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  easily,  coating  the  charcoal  with  white  oxide.  In 
R.  I.  is  reduced,  but  again  oxidizes  and  coats  the  coal,  coloring  the  flame  green.  Solu- 
ble in  hydrochloric  acid. 

REMARKS. — Occurs  in  quantity  in  radiated  form  at  Ain  Bebbouch,  Algiers;  and 
massive  at  Kostainik,  Servia.  In  other  localities  as  Rosia,  Tuscany;  Braunsdorf, 
Saxony,  in  crystals. 

SENARMONTITE. 

COMPOSITION. — Sb2O3,  (Sb,  83.3  per  cent.). 

GENERAL  DESCRIPTION. — Colorless  to  gray  octahedral  crystals  and  granular 
masses. 

PHYSICAL  CHARACTERS. — Transparent  to  translucent.  Lustre,  resinous.  Color, 
colorless  or  gray.  Streak,  white.  H.,  2  to  2.5.  Sp.  gr.,  5.22  to  5.30. 

BEFORE  BLOWPIPE,  ETC. — Like  valentinite. 

REMARKS. — Occurs  as  large  replacement  deposit  in  clay  and  limestone  at  Djebel- 
Hamimat,  Algeria.  Elsewhere  chiefly  as  small  crystals  on  other  antimony  minerals 
as  at  Kostainik,  Servia,  and  Wolfe  Co.,  Quebec. 

ANTIMONY  OCHRE. 
Cervantite  and  Stibiconite. 

COMPOSITION. — Cervantite,  Sb2O4,  Stibiconite,  Sb2O4,  H2O. 

GENERAL  DESCRIPTION. — Pale  yellow  to  reddish  white,  masses,  crusts  and  powder 
with  greasy  lustre  or  dull.  Streak  white.  H.,  4  to  5.5.  Sp.  gr.,  4.08  to  5.28. 


336  MINERALOGY. 

BEFORE  BLOWPIPE,  ETC. — Infusible  in  forceps.  Stibiconite  yields  water  in  closed 
tube,  decrepitates  and  fuses  on  charcoal.  Cervantite  yields  no  water,  and  on  charcoal 
is  easily  reduced. 

REMARKS. — These  species  are  the  common  result  of  the  oxidation  of  antimony 
deposits  and  usually  occur  together  as  in  Borneo.  The  extensive  deposits  in  Sonora, 
Mexico  and  the  upper  60  feet  of  the  Pricov,  Bohemia,  deposit  are  called  stibiconite 
while  others  as  at  Pereta,  Tuscany,  are  called  cervantite. 

THE  VANADIUM   MINERALS. 

The  minerals  described  are: 

Sulphide       Patronite  VS4(?) 

Vanadates     Vanadinite  Pb5Cl(VO4)3  Hexagonal 

Descloizite  (PbZn)2(OH)VO4  Orthorhombic 

Hewettite  and  Metahewettite  CaO,  3V2O5.9H2O 

Silicates        Roscoelite  Vanadium  Mica 

Other  minerals  containing  vanadium  are  carnotite,  and  the 
briefly  described  and  in  part  indefinite  species  mottramite,  psitta- 
cinite,  dechenite,  volborthite,  pucherite,  and  pascoite. 

ECONOMIC    IMPORTANCE. 

It  was  proved*  in  1830  that  the  unusual  ductility  of  the  iron 
made  from  the  Taberg,  Sweden,  ores  was  due  to  the  vanadium  in 
the  ores.  Since  that  the  use  of  vanadium  in  iron  and  steel  has 
slowly  increased. 

Iron  castings  are  made  by  vanadium  finer  grained  and  less 
porous. 

It  removes  oxygen  and  nitrogen  from  steel  and  the  combined 
effect  of  this  and  a  small  amount  (0.15  to  0.25  per  cent.)  retained 
in  the  steel  enormously  increases  the  tensile  strength  and  thereby 
the  resistance  to  shock  and  abrasion.  Vanadium  steel  is  increas- 
ingly used  for  steel  castings  for  locomotives,  automobiles,  die 
blocks,  heavy  drop  forge  work,  etc. 

Tough  alloys  are  made  with  copper,  such  as  vanadium  bronze 
much  used  for  trolley  wheels,  bronze  gearing,  etc. 

The  oxide  V2O5  is  used  in  place  of  platinum  as  a  catalytic  agent 
in  the  manufacture  of  sulphuric  acid  and  other  processes  and 
with  aniline  as  a  black  dye  and  in  making  an  indelible  ink. 

This  country  produced  in  1914  carnotite  and  roscoelite  ore  con- 
taining 452  tons  of  vanadium.f  The  great  source,  however,  is  the 

*  Mining  World,  1905,  p.  659. 

f  Mineral  Resources  U.  S.  1914,  p.  14. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.      337 

patronite  of  Peru,  which  is  oxidized  and  reduced  either  with 
Thermit  or  in  the  electric  furnace  to  form  ferro-vanadium. 

Roscoelite  is  roasted  with  salt,  the  sodium  vanadate  extracted 
with  water,  ferrous  sulphate  added  and  the  precipitated  iron 
vanadate  reduced  in  the  electric  furnace.  The  product  is  a  ferro- 
vanadium  containing  25  to  50  per  cent,  of  vanadium.  The  proc- 
ess for  vanadinite,  now  of  relatively  little  importance,  involved 
previous  extraction  of  the  lead  by  reduction  with  carbon  and 
sodium  carbonate,  the  slag  being  treated  as  above. 

In  the  production  of  radium  from  carnotite,  the  vanadium  re- 
mains in  solution  as  sodium  vanadate  from  which  it  is  precipitated 
by  ferrous  sulphate. 

THE    FORMATION   AND    OCCURRENCE    OF   VANADIUM    DEPOSITS. 

Vanadium  is  not  a  rare  element,  it  occurs  in  small  amounts  in 
many  igneous  rocks  as  V2O3  up  to  .O3-.O5  per  cent,  replacing 
Fe2O3  and  Al2Os  in  some  pyroxenes  (up  to  2  per  cent.)  amphiboles 
and  micas  and  is  almost  invariably  present  in  magmatic  deposits 
of  titaniferous  iron.*  (5  analyses  average  0.27  per  cent.)  Not- 
ably the  ore  of  Taberg,  Sweden. 

Sediments. 

After  weathering  of  the  igneous  rocks  the  vanadium  is  con- 
centrated in  the  resulting  clays,  sandstones  (many  of  the  copper- 
bearing  standsones  carry  vanadium)  and  beds  of  iron  ore  and  eco- 
nomically important  deposits  have  resulted  as  in  the  sandstones 
of  Colorado  and  Utah,  Cheshire,  England,  and  Perm,  Russia,  and 
the  oolitic  limonites  of  Mafenay,  France.  It  is  found  in  the  baux- 
ites and  clays  near  Paris. 

The  ash  of  lignites  from  San  Rafael,  Mendoza,  Argentina  and 
Yauli,  Peru,  contain  about  38  per  cent,  of  V2O5,  and  the  asphalt 
grahamite  of  West  Virginia  and  Oklahoma  carries  vanadium;  the 
great  deposit  of  vanadium  sulphide  in  Cerro  de  Pasco  is  in  large 
part  an  asphalt  containing  a  large  amount  of  sulphur. 

Veins. 

Vanadium  also  occurs  in  ore  veins  and  ore  bodies,  notably  with 
gold  as  the  vanadium  mica  roscoelite  as  a  primary  mineral  but  more 
frequently  as  lead  or  copper  vanadates  in  the  oxidized  portions. 

*  Clarke,  Bull.  491,  673. 
23 


338 


MINERALOGY. 


PATRONITE. 

COMPOSITION.— VS4(?),  (58.79  S,  19.53  V,  1.87  Ni,  3.47  C,  per 
cent.). 

GENERAL  DESCRIPTION. — Greenish  black,  resembling  slaty  coal, 
consisting  of  the  vanadium  sulphide  mixed  with  metallic  sulphides 
chiefly  a  nickel  bearing  pyrite  (bravoite)  and  free  sulphur.  H. 
3.5  and  2.5.  Sp.  gr.  2.5  and  2.71. 

BEFORE  BLOWPIPE,  ETC. — No  record  has  yet  been  made  of  its 
blowpipe,  etc.,  characters.  On  roasting  it  yields  the  recorded 
test,  p.  196,  with  hydrochloric  acid. 

REMARKS.* — Found  only  as  a  lens-shaped  mass  28  feet  wide  by  350  feet  long, 
filling  a  fault  in  red  shales  (Cretaceous)  at  Minisraga,  Cerro  de  Pasco,  Peru.  The 
larger  portion  of  the  mass  (called  quisqueite  H.  2.5,  sp.  gr.,  1.75)  is  a  lustrous  black 
asphalt-like  material  with  more  sulphur  than  carbon  which  blends  in  a  coke-like 
material  86  per  cent,  carbon  (H.  4.5,  sp.  gr.  2.2).  Below  the  lode  is  a  blue  black  shale 
containing  up  to  13  per  cent,  vanadium  oxide.  The  ore  is  burned  and  the  ashes 
carrying  the  vanadium  exported. 

VANADINITE. 


V 


VAIN  AUJ.  mil!*. 

COMPOSITION.— 3Pb3(VO4)2.PbCl2  or  Pb5Cl(VO4)3,  (PbO,  78.7; 
2O5,  194;  Cl,  2.5  per  cent.),  often  with  P  or  As  replacing  V. 


FIG.  378. 


FIG.  379. 


GENERAL  DESCRIPTION. — Small,  sharp,  hexagonal  prisms,  some- 
times hollow,  of  bright-red,  yellow  or  brown  color.  Also  parallel 
groups  and  globular  masses  of  crystals. 

CRYSTALLIZATION. — Hexagonal.  Class  third  order  pyramid, 
p.  57.  Axis  c  =  0.712.  Simple  prism  m  with  base  c,  or  more 
rarely  with  pyramid  p  and  third  order  pyramid  v  =  (fa  :  2>a  :  a: 
3c);  {2131},  Fig.  379. 


*  See  Jour.  Am.  Chem.  Soc.,  29,  1907,  July,  Trans.  Am.  Inst.  Min.  Eng.,  1909,  292. 
Bulletin  70,  Bureau  Mines,  p.  55. 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.      339 

Physical  Characters. — H.,  3.     Sp.  gr.,  6.66  to  7.23. 

LUSTRE,  resinous  on  fracture.  OPAQUE,  or  translucent. 

STREAK,  white  to  pale  yellow.  TENACITY,  brittle. 

COLOR,  deep  red,  bright  red,  yellow  or  brown. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  on  charcoal  to  a  black 
mass,  yielding  a  yellow  sublimate  in  the  reducing  flame.  The 
residue  gives  deep-green  bead,  with  salt  of  phosphorus  in  the  re- 
ducing flame.  With  strong  nitric  acid  the  substance  becomes  deep 
red,  then  dissolves  to  a  yellow  solution.  Fused  with  KHSCX, 
yields  a  clear  yellow,  then  a  red,  and  finally  yellow  when  cold. 

VARIETIES. — Endlichite.     The  V2O5  replaced  in  part  by  As2O5. 

REMARKS. — Vanadinite  occurs  in  the  oxidized  zone  of  lead-bearing  veins  in  many 
localities  especially  New  Mexico  and  Arizona.  Sometimes  the  quantity  is  worth 
concentrating  as  at  the  Mammoth  Gold  Mine,  Arizona,  and  Cutter,  Sierra  Co.,  N.  M. 
Descloizite  and  wulfenite  are  common  associates.  Foreign  localities  are  Dumfries- 
shire, Scotland,  on  calamine,  Berezof  Urals  with  pyromorphite. 

The  variety  endlichite  is  reported*  in  quantity  in  Baraga  Co.,  Michigan,  the  ore 
showing  21.5  per  cent,  vanadium. 

DESCLOIZITE. 

COMPOSITION.— (Pb.Zn)(PbOH),  VO4,  (PbO,  55-4J  ZnO,  19.7;  V2O6,  22.7; 
H20,  2.2). 

GENERAL  DESCRIPTION. — Small  purplish-red,  brown  or  black  crystals,  forming 
a  drusy  surface  of  crust.  Also  fibrous,  massive. 

PHYSICAL  CHARACTERS. — Transparent  to  nearly  opaque.  Luster,  greasy.  Color, 
purplish  red,  brown  or  black.  Streak,  orange  or  brown.  H.,  3.5.  Sp.  gr.,  5.9  to  6.2. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses  to  black  mass,  enclosing  metal. 
In  closed  tube  yields  water.  Vanadium  reactions  as  in  vanadinite. 

VARIETIES. — Cuprodescloizite  in  crusts  and  reniform  masses  with  radiated  structure 
contains  6.5  to  9  per  cent,  copper. 

REMARKS. — Descloizite  is  a  frequent  associate  of  vanadinite  and  at  the  Mammoth 
Gold  Mine,  Arizona,  and  the  Mimbres  Mine  near  Georgetown,  New  Mexico,  was  more 
plentiful  than  the  vanadinite.  In  Sierra  de  Cordoba,  Argentina,  occurs  with 
pyromorphite  and  vanadinite. 

The  variety  cuprodescloizite  has  been  found  in  considerable  quantities  at  Charcas, 
San  Luis  Potosi  and  Zacatecas,  Mexico,  and  near  Bisbee,  Arizona;  also  in  Otavi, 
German  East  Africa. 

Less  important  vanadates  are: 

MOTTRAMITE  (CuPb)5V2Oio  2H2O).  Thin,  blackish  green  incrustations  upon 
the  Keuper  sandstone  at  Mottram,  St.  Andrews,  Cheshire,  England.  Streak  yellow, 
H  =  3,  G  =  5-9- 

PSITTACINITE. — 4(CuPb)O.V2O6H2O,  thin  greenish  incrustations  on  quartz  in 
Silver  Star  District,  Montana.  Also  Laurium,  Greece. 

*  Mineral  Industry,  1914,  p.  762. 


340  MINERAL  OGY. 

DECHENITE.  —  PbV^Oe.  Massive  botryoidal  red  to  yellow.  Streak  orange 
yellow.  H.,  3  to  4.  Sp.  gr.  5.6  to  5.8  from  Lauterthal,  Prussia. 

VOLBORTHITE.—  (Cu.Ca.Ba)3(OH)3VO4  in  six-sided  green  to  yellow  tables. 
Streak  yellowish  green.  From  Urals  and  Utah. 

PUCHERITE.  —  BiVO4  in  druses  of  small  orthorhombic  crystals  of  reddish  brown 
color.  Streak  yellow.  From  Schneeberg,  Saxony. 

HEWETTITE   AND    METAHEWETTITE. 


COMPOSITION.  —  CaO.3V2O5.9H2O.  (V2O6  70.01,  V2O3  0.35,  CaO  7.25,  H2O  21.30 
per  cent.). 

GENERAL  DESCRIPTION.  —  Both  occur  as  reddish  earthy  powders  from  mahogany 
red  to  brownish  red  the  hewettite  being  the  brighter.  Hewettite  also  occurs  in 
mahogany  red  needles  and  metathewettite  in  aggregates  of  highly  pleochroic  scales. 
Sp.  gr.,  2.554;  hewettite,  2.511  metahewettite. 

BEFORE  BLOWPIPE,  ETC.  —  Both  darken  on  heating  and  as  water  escapes  again 
grow  lighter  in  color  ending  bronze  (hewettite)  or  yellow  brown  (metahewettite). 
Melt  easily  to  a  dark  red  liquid.  Both  slightly  soluble  in  water  and  yield  the  de- 
scribed test,  p.  196,  with  hydrochloric  acid. 

REMARKS.  —  Hew.ttite  occurs  in  pockets  and  fissures  of  a  shale  overlying  patronite. 
Metahewettite  is  the  chief  constituent  of  a  red  vanadium  ore  from  Paradox  Valley, 
Montrose  Co.,  Colorado,  and  through  a  wide  area  to  Thompson,  Utah.  Occurs  as  an 
impregnation  of  sandstone.  At  Thompson  it  is  associated  with  a  gray  vanadium- 
bearing  silicate  and  with  particles  of  selenium. 

PASCOITE  is  2CaO.3V2Os.nH2O  in  orange  red  thin  plates  (monoclmic)  some- 
what adamantine  lustre.  An  alteration  of  patronite  not  observed  in  the  surface 
.deposit  at  Minisraga  but  has  formed  since  on  the  walls  of  an  exploratory  tunnel. 

ROSCOELITE.  —  Vanadium  Mica. 

COMPOSITION.  —  Doubtful,  V2O3  replacing  A12O3  in  muscovite 
formula  perhaps.  Percentage  of  V2O3  very  variable,  sometimes 
20-29  per  cent. 

GENERAL  DESCRIPTION.  —  Minute  scales  with  micaceous  cleav- 
age dark  green  to  brown  in  color  suggesting  a  chlorite.  Lustre 
pearly.  H.,  2.  Sp.  gr.,  2.92  to  2.94. 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  easily  to  a  black  glass.  Essen- 
tially insoluble  in  acids.  Gives  emerald  green  bead  in  R.  F.  with 
salt  of  phosphorus  after  fusion  with  sodium  carbonate  gives  the 
described  test,  p.  196,  with  hydrochloric  acid. 

Remark?.  —  Occurs  as  primary  mineral  in  gold  veins  in  Granite  Creek,  California, 
and  with  gold  telluride  at  the  Magnolia  District,  Colorado.  Near  Newmire  and 
Placerville,  on  both  sides  of  Bear  creek  in  San  Miguel  Co.,  Colorado,  as  an  impreg- 
nation of  a  fine-grained  sandstone  showing  as  a  dull  green  band  nearly  parallel 
to  the  bedding.  Although  averaging  only  i}^  Per  cent.  V2O5  is  mined  at  a 
profit. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.      341 

THE   URANIUM   AND   RADIUM   MINERALS. 

The  minerals  described  are : 

Uranate  Uraninite  Uranyl  uranate  2UO3.UO2(?)  Isometric 

Vanadate  Carnotite  (K2Ca)2UO3.V2O53H2O(?) 

Phosphates  Autumte  Ca(UO2)2(PO4)2.8H2O  Orthorhombic 

Torbernite  Cu(UO2)2(PO4)2.8H2O  Tetragonal 

Coracite,  and  gummite  and  uraconite  are  mentioned  briefly 
after  uraninite,  uvanite  after  carnotite.  Uranium  is  also  present 
in  the  described  species  thorianite,  thorite,  fergusonite,  samarskite, 
euxenite,  polycrase,  and  xenotime,  and  in  a  large  series*  of  phos- 
phates, carbonates,  arsenates,  sulphates  and  silicates. 

ECONOMIC   IMPORTANCE. 

The  metal  uranium  has  a  limited  use  in  uranium  steel,  as  a  small 
percentage  of  uranium  increases  the  elasticity  and  hardness  of  or- 
dinary steel. 

A  few  tons  of  sodium  uranate,  commercially  known  as  uranium 
yellow,  are  used  each  year  in  coloring  glass  yellow  with  a  greenish 
reflex,  and  in  coloring  porcelain  orange  or  black.  A  small  amount 
is  used  in  photography  and  in  the  manufacture  of  uranium  salts 
important  in  the  laboratory. 

Aside  from  this  the  importance  of  uranium  lies  in  its  use  for 
the  extraction  of  radium  which  is  always  with  uranium  in  amount 
proportionate  to  the  uranium  present. 

The  ratio  is  constant  for  old,  unaltered  minerals  and  has  been 
calculated  as: 

Ra 

—  =  3.4  X  io-7. 

That  is,  from  I  gm.  U  there  would  develop  .00000034  gm.  radium 
(or  i  gm.  Ra  from  3,000,000  gm.  U),  thereafter  there  would  be 
equilibrium. 

If,  however,  the  mineral  is  relatively  young  and  secondary  or  if 
it  has  been  altered  by  percolating  waters  and  one  or  more  of 
products  removed  equilibrium  may  not  exist  and  the  ratio  be  different. 

Many  tons  of  uraninite  have  been  worked  over  to  obtain  a  few  grams  of  impure 
radium  chloride,  the  remarkable  properties  of  which  are  being  widely  studied.  It 

*  See  Bulletin  70,  Bureau  of  Mines,  p.  92.  Some  of  species  are  sulphate,  johan- 
nite,  arsenate,  trogerite,  silicate  uranophane,  phosphate  fritzscheite,  carbonate, 
liebigite. 


342  MINER  ALOG  Y. 

seems  probable  that  there  is  here  the  first  known  instance  of  the  decomposition  of  the 
chemical  atom,  for  radium  gives  off  helium  apparently  as  a  decomposition  product, 
and  with  the  evolution  of  an  amount  of  energy  far  beyond  any  previous  conception. 
It  also  is  continually  throwing  off  emanations  or  rays  which  affect  a  photographic 
plate  and  discharge  an  electroscope.  Some  of  these  too  are  of  a  material  character. 
Still  years  must  elapse  before  any  loss  of  weight  can  be  detected  by  the  most  delicate 
balance. 

The  uses  of  radium  are  in  scientific  research  and  in  medicine, 
though  in  the  latter  the  results  are  still  uncertain.  Good  results 
are  claimed  in  treatment  of  lupus,  skin  diseases,  and  some  forms 
of  cancer  and  it  is  said  to  have  favorable  results  on  rheumatism. 

Baths  have  been  established  by  the  Austrian  government  at 
St.  Joachimsthal  which  are  recommended  for  rheumatism,  neural- 
gia, chronic  eczema,  etc. 

Radium  has  been  proved  in  a  number  of  cases  to  change  the 
color  of  minerals  such  as  diamond  and  sapphire. 

The  three  minerals  which  are  important  commercial  sources  of 
uranium  and  radium  are  carnotite,  uraninite  and  autunite,  and 
smaller  amounts  may  be  credited  to  uvanite  and  torbernite. 

The  production*  in  1914  in  the  United  States  was  4,294  tons  of 
ore,  carrying  87.2  tons  of  U3Os  and  22.3  grams  of  metallic  radium, 
chiefly  from  carnotite  from  Colorado  and  Utah  but  some  from 
uvanite  from  the  Henry  Mountains,  Utah. 

Other  sources  were  uraninite  from  Cornwall,  Austria  and  the 
mines  of  Colorado,  of  carnotite  from  Olary,  Australia,  and  of 
autunite  from  Guarda,  Portugal. 

Uraninite  is  roasted  with  sodium  carbonate  and  nitrate,  leached  with  water  and 
the  residues  treated  with  sulphuric  and  nitric  acids,  giving  uranyl  sulphate,  from 
which  other  salts  are  made. 

Ores  containing  both  uranium  and  vanadium  (carnotite,  uvanite)  are  usually 
subjected  to  wet  treatment,  boiled  with  a  solution  of  sodium  or  potassium  carbonate 
or  treated  with  dilute  sulphuric  acids.  At  other  times  it  is  roasted  with  salt  or  fused 
with  acid  potassium  sulphate  and  leached  with  water. 

The  uranium  salts  are  in  the  solution  and  are  suitably  precipitated,  the  radiumf 
is  in  the  residues  from  which  it  and  barium  are  obtained  together  and  separated  by 
fractional  crystallization  based  on  the  difference  in  solubility  of  their  chlorides. 

FORMATION   AND    OCCURRENCE   OF   URANIUM    DEPOSITS. 
Uranium  is  found  in  granitic  rocks  and  their  pegmatites  usually 
with  tungsten,  in  small  amounts  chiefly  as  crystalline  uraninite. 

*  Mineral  Resources  U.  S.  1914,  p.  14. 
t  See  Bull.  70,  Bureau  of  Mines,  69  to  82. 


MINERALS    OF  METALLIFEROUS    ORE  DEPOSITS.     343 

Veins. 

Important  deposits  are  generally  in  veins,  the  primary  mineral 
being  usually  the  amorphous  variety  of  uraninite  pitchblende. 

In  Tin  Veins. — In  Cornwall  and  Devon  in  several  veins,  espe- 
cially one  at  Grampound.* 

In  Silver  Nickel  Cobalt  Veins. — In  the  Erzgebirge,  especially  at 
Joachimsthal,  Bohemia,  near  but  not  with  tin,  in  slates  near 
granite. 

In  Silver  Gold  Veins. — In  Gilpin  Co.,  Col.  (Wood  mine,  Kirk 
mine,  etc.),  in  gneiss  and  mica  schist  with  silver-  and  gold-bearing 
pyrite  and  chalcopyrite. 

Sedimentary. 

Uranium  minerals,  especially  carnotite,  occur  concentrated  in 
the  Dakota  sandstone  in  Utah  and  Colorado.  In  Utah,  where  it 
has  in  part  replaced  the  original  calcite  cement,  at  other  times 
appears  in  fissures  or  funnel-shaped  cavities.  Fossil  remains  are 
frequent  and  the  carnotite  is  abundant  in  and  near  them. 

URANINITE.— Pitchblende. 

COMPOSITION. — Uranyl  uranate  and  may  contain  Ca,  N,  Th, 
Zr,  Fe,  Cu,  Bi,  etc. 

GENERAL  DESCRIPTION. — A  black  massive  mineral  of  botryoidal 
or  granular  structure  and  pitch-like  appearance.  Rarely  in  small 
isometric  crystals. 

Physical  Characters.     H.,  5.5.     Sp.  gr.,  6.5  to  9.7. 

LUSTRE,  pitch-like,  submetallic.  OPAQUE. 

STREAK,  gray,  olive  green,  dark  brown.       TENACITY,  brittle. 

COLOR,  some  shade  of  black. 

BEFORE  BLOWPIPE,  ETC. — Infusible  or  very  slightly  fused  on 
edges,  sometimes  coloring  the  flame  green  from  copper.  On  char- 
coal with  soda  may  yield  reaction  for  lead,  arsenic  and  sulphur.  In 
borax  yields  a  green  bead  made  enamel  black  by  flaming.  Soluble 
in  nitric  acid  to  a  yellow  liquid  from  which  ammonia  throws  down 
a  bright  yellow  precipitate.  See  also  p.  195. 

SIMILAR  SPECIES. — The  appearance  and  streak  are  frequently 
sufficient  distinctions.  The  bead  tests  are  characteristic. 

*  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  713. 


344  MINERAL  OG  Y. 

VARIETIES. — Crystallized.  The  crystals  of  the  granites  and 
their  pegmatites  are  complex  in  composition  and  often  carry  rare 
earths  and  nitrogen,  because  of  which  other  names  have  been 
given  such  as  cleveite,  nivenite,  broggerite,  uranniobite. 

Pitchblende. — The  uraninite  of  the  ore  veins  appears  to  be  of 
colloidal  origin;  it  contains  no  rare  earths  and  little  nitrogen, 
but  contains  water  and  is  often  intermixed  with  metallic  sulphides. 

Coracite. — Partially  altered  uraninite. 

REMARKS. — The  important  variety  pitchblende  occurs  in  veins  as  stated  p.  343, 
another  important  deposit  being  the  Vereinigt  Mine  at  Johanngeorgenstadt,  Saxonyr 
Coracite  occurs  north  of  Sault  Ste.  Marie. 

The  crystallized  variety  occurs  in  pegmatites  as  at  Branchville,  Conn.,  Annerod, 
Norway,  Mitchell  and  Yancy  Cos.,  North  Carolina.  Nodular  material  occurs  in  a 
pegmatite  at  Abraki  Pahai,  India. 

GUMMITE. — An  alteration  of  uraninite  of  doubtful  composition  but  with  61-75 
per  cent,  of  UOs  occurs  in  rounded  and  flattened  gum-like  masses  of  reddish  yellow 
to  red  or  brownish  color.  H.,  2.5,  sp.  gr.,  4.  Principal  locality,  the  Flat  Rock 
Mine,  Mitchell  Co.,  N.  C.,  but  also  Texas,  and  Joachimsthal,  Bohemia. 

CARNOTITE. 

COMPOSITION.— (K2,  Ca)O,  2UO3,  V2O5  +  H2O.  (?)  It  is  pro- 
posed to  use  the  name  carnotite  for  the  potassium  compound  and 
tyuyamunite  for  the  calcium  compound. 

GENERAL  DESCRIPTION. — Usually  a  canary  yellow  or  lemon 
yellow  material,  but  sometimes  red  or  black.  Sometimes  in 
loosely  cohering  masses  of  minute  scales,  oftener  disseminated, 
filling  interstices  in  sandstone.  Rarely  compact  and  wax-like. 

CRYSTALLIZATION. — Under  the  microscope  shows  rhombic  plates 
with  basal  cleavage  and  rhombic  symmetry. 

BEFORE  BLOWPIPE,  ETC. — Easily  soluble  in  hydrochloric  or 
nitric  acid. 

REMARKS. — Occurs  as  stated  p.  343,  in  sandstone  in  Colorado  and  Utah,  notably 
in  Paradox  Valley,  Colorado,  and  San  Juan  Co.,  Utah. 

The  Utah  deposits  carry  less  carnotite  and  the.  ore  varies  more  in  color  than  the 
deposits  of  Colorado.  Further  east,  as  at  Placerville,  the  carnotite  is  small  in  amount 
•  and  the  dominant  species  is  roscoelite. 

Carnotite  in  small  amounts  is  found  in  crevices  in  a  granite,  at  Olary,  South  Aus- 
tralia, and  a  large  deposit  is  reported  under  the  name  ferghanite  at  Ferghana,  Russian 
Turkestan. 

UVANITE,  2UO3,  3V2O5.i5H2O  is  a  recently  described  brownish-yellow  hydrous 
uranium  vanadate  resembling  carnotite  in  appearance  and  occurring  in  economic 
quantities  at  Temple  Rock,  Emery  Co.,  Utah. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS,      345 

AUTUNITE.— Lime  Uranite. 

COMPOSITION.— Ca(UO2)2(PO4)2  +  8H2O,  (UO3  63.7,  CaO  6.1,  P2O6  15.5,  H2O  15.7 
per  cent.). 

GENERAL  DESCRIPTION. — Nearly  square  (90°  43')  orthorhombic  plates  of  bright 
yellow  color  and  pearly  lustre,  or  in  micaceous  aggregates. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  pearly  on  base.  Color,  lemon  to 
sulphur  yellow.  Streak,  pale  yellow.  H.,  2  to  2.5.  Sp.  gr.,  3.05  to  3.19.  Brittle. 
Cleavage  basal. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  with  intumescence  to  a  black  crystal- 
line globule.  With  salt  of  phosphorus  or  borax  in  the  reducing  flame  yields  a  green 
bead.  Dissolves  in  nitric  acid  to  a  yellow  solution. 

REMARKS. — The  only  deposit  of  economic  importance  is  in  northern  Portugal. 
The  veins  are  in  granite  and  schist  and  are  richest  near  Guarda  in  Beira.  The  vein 
material  is  largely  quartz  and  feldspar  with  clay  and  the  autunite  is  disseminated. 
Torbernite  is  present  and  in  the  vicinity  are  veins  carrying  tungsten,  tin,  galena,  etc. 

Occurs  in  many  localities  in  small  amounts. 

TORBERNITE. — Copper  Uranite. 

COMPOSITION.— Cu(UO2)2(PO4)2  +  8H2O,  (UO3  61.2,  CuO  8.4,  P2O5  15.1,  H2O 
15.3  per  cent.). 

GENERAL  DESCRIPTION. — Thin  square  tetragonal  plates  of  bright  green  color  and 
pearly  lustre.  Sometimes  in  pyramids  or  micaceous  aggregates. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  pearly.  Color,  emerald  to  grass 
green.  Streak,  pale  green.  H.,  2  to  2.5.  Sp.  gr.,  3.4  to  3.6.  Brittle. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  to  a  black  mass  and  colors  the  flame  green. 
In  borax  yields  a  green  glass  in  O.  F.,  which  becomes  opaque  red  in  R.  F.  Soluble 
in  nitric  acid  to  a  yellowish-green  solution. 

REMARKS. — The  deposit  of  autunite  at  and  near  Guarda,  Portugal,  contains 
torbernite  and  a  deposit  reported  near  Farina,  South  Australia,  is  principally  torber- 
nite.  Other  localities  are  Cornwall,  England,  and  Joachimsthal,  Bohemia. 

THE   CHROMIUM   MINERALS. 

The  minerals  described  are  : 

Chromite  FeCr2O4  Isometric 

Crocoite  PbCrO4  Monoclinic 

Spinel,  chrysolite,  serpentine,  pyroxene,  mica,  garnet,  chlorite, 
etc.,  have  chromium-bearing  varieties,  and  there  are  chromium- 
bearing  clays*  and  a  few  unimportant  chromates.t 

ECONOMIC   IMPORTANCE. 

The  only  commercial  ore  is  chromite.  This  country  produced 
in  1915^  3,281  long  tons,  chiefly  from  Shasta  and  Fresno  counties, 

%  Mineral  Resources,  U.  S.,  1915,  pt.  i,  p.  2. 

*  Wolchonskoite,  miloschite,  chrome  ochre. 
t  Phoenicochroite,  vauquelinite,  tarapacaite. 


346  MINERAL  OGY. 

California.     In   the  same  period   this  country  imported   76,455 
tons  as  follows : 

Exported  to  U.  S.  Total  Output 

New  Caledonia 28,031  67,000 

Rhodesia 22,800  57,333 

Portugese  Africa 11,230 

Canada 10,087 

Greece 4,305 

Turkey,  Russ'a,  Japan  and  India  are  also  producers. 

The  most  important  use  is  the  manufacture  of  sodium  and 
potassium  bichromate  and  chromate,  used  in  calico  printing, 
electric  batteries,  the  chrome  colors  and  pigments,  etc.  Chromite 
is  also  used  in  the  manufacture  of  ferrochrome,  which  in  turn  is 
used  in  making  chrome  steel,  much  used  for  high  speed  tools, 
armor  plate  and  projectiles  which  possesses  great  hardness  and 
resistance  to  impact. 

Mixed  with  a  suitable  binder  chromite  is  made  into  highly 
refractory  bricks  for  copper  and  steel  furnaces. 

Ferrochrome  is  made  in  the  electric  furnace. 

FORMATION  AND  OCCURRENCE  OF  CHROMIUM  DEPOSITS. 

The  only  ore  of  chromium  is  chromite  and  all  known  deposits 
of  chromite  occur  in  peridotite  or  the  serpentine  derived  from  it,* 
almost  entirely  as  magmatic  segregations,  occasionally  as  secon- 
dary chromite  by  alteration  of  chromium-bearing  silicates. 

Magmatic  Segregations. 

The  earth's  crust  contains,  it  is  estimated,  .01  per  cent,  of 
chromium  but  the  peridotites  contain  generally  0.2  to  0.5  per  cent, 
and  up  to  I  per  cent.f  of  Cr2O3  and  the  segregations  up  to  60  per 
cent,  chiefly  as  chromite  but  also  as  chrome  spinel  (picotite)  and 
the  chromium-bearing  silicates  mentioned  on  last  page. 

The  deposits  may  be  in  essentially  unaltered  peridotite  as  at 
the  Island  of  Hestmando,  Norway;  Mt.  Dun,  New  Zealand,  or 
Kraubat,  Styria;  or  they  may  be  in  serpentine  rock  as  at  Feragen, 
Norway,  Tirbaghi  Hills  and  Mt.  Dere,  New  Caledonia;  Thetford, 
Canada;  Selukwe  and  Beira,  Rhodesia. 

*  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  244. 
t  Beyschlag,  Vogt  und  Krusch  (Truscott),  p.  244. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.      347 

Secondary  Deposits. 

Secondary  deposits  of  chromite  due  to  the  decomposition  of 
chrome-bearing  silicates  are  reported  in  Bosnia. 

Residual  Deposits. 

Chromite  being  very  resistant  to  atmospheric  influences  is  very 
common  in  gravels,  these  forming  part  of  the  New  Caledonia 
deposits  and  at  one  time  utilized  from  the  Ural  platinum  deposits. 

CHROMITE.— Chromic  Iron. 

COMPOSITION. — FeCr2O4,  (FeO  32,  Cr2O3  68  per  cent),  some- 
times with  A12O3  or  MgO  as  replacing  elements. 

GENERAL  DESCRIPTION. — Usually  a  massive  black  mineral  resem- 
bling magnetite.  Occurs  either  granular  or  compact  or  as  dissem- 
inated grains.  Rarely  in  small  octahedral  crystals.  Frequently 
with  more  or  less  serpentine,  mechanically  intermixed,  giving  rise 
to  green  and  yellow  spots  and  streaks. 

Physical  Characters.     H.,  5.5.     Sp.  gr.,  4.3  to  4.6. 
LUSTRE,  sub- metallic  to  metallic.  OPAQUE. 

STREAK,  dark-brown.  TENACITY,  brittle. 

COLOR,  black.  May  be  slightly  magnetic. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  sometimes  slightly  fused  by 
reducing  flame,  and  then  becomes  magnetic.  In  salt  of  phos- 
phorus, in  oxidizing  flame,  gives  yellow  color  hot,  but  on  cooling 
becomes  a  fine  emerald-green.  With  soda  and  nitre  on  platinum 
fuses  to  a  mass,  which  is  chrome-yellow  when  cold.  Insoluble  iu 
acids. 

SIMILAR  SPECIES. — Chromite  is  distinguished  from  other  black 
minerals  by  the  salt  of  phosphorus  reactions,  and  to  a  consider- 
able extent  by  the  serpentine  with  which  it  occurs. 

REMARKS. — Occurs  as  described,  p.  346.  In  this  country  the  Woods  Mine,  near 
Baltimore,  furnished  from  1828  to  1850  most  of  the  ore  used  by  the  world,  the  rest 
coming  from  the  platinum  deposits  of  the  Urals.  Later  deposits  were  worked  in 
Lancaster  County,  Pa.,  and  in  California  and  the  latter  are  still  worked. 

CROCOITE. 

COMPOSITION.— PbCrO4,    (PbO,  68.9  ;  CrO3,  31.1  per  cent.). 

GENERAL  DESCRIPTION. — Bright  hyacinth-red  mineral,  usually  in  monoclinic  pris- 
matic crystals,  but  also  granular  and  columnar.  The  color  is  like  that  of  potassium 
dichromate. 


348  MINERALOGY. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  adamantine.  Color,  hyacinth 
red.  Jtreak,  orange  yellow.  H.,  2.5  to  3.  Sp.  gr.,  5.9  to  6.1.  Sectile.  Cleavage, 
prismatic. 

BEFORE  BLOWPIPE,  ETC. — In  closed  tube,  decrepitates  violently,  becomes  dark,  but 
recovers  color  on  cooling.  Fuses  very  easily,  and  is  reduced  to  metallic  lead  with, 
.deflagration,  the  coal  being  coated  with  a  yellow  sublimate.  With  borax  or  S.Ph., 
forms  yellow  glasses,  which  are  bright  green  when  cold.  Soluble  in  nitric  acid  to  a 
yellow  solution.  Fused  with  KHSO4  in  closed  tube,  yields  a  dark-violet  mass,  red  on 
solidifying  and  greenish-white  when  cold,  which  distinguishes  it  from  vanadinite. 

REMARKS. — Chromium  was  discovered  in  samples  of  this  mineral  by  Vauquelin 
in  1797.  It  occurs  in  lead-bearing  veins  in  gneiss  and  granite  in  Berezof,  Mursinska 
and  Nischni  Tagilsk,  Urals.  Similarly  in  Hungary  and  Brazil.  Fine  crystals  come 
from  the  Broken  Hill  Mine,  Australia.  It  is  nowhere  found  in  commercial  quantities. 

THE   MOLYBDENUM   MINERALS. 

The  minerals  described  are : 

Sulphide  Molybdenite  MoS2  Hexagonal 

Oxide  Molybdite  MoOs  Orthorhombic 

Wulfenite  PbMoO4  Tetragonal 

Other  molybdates*  are  powellite,  CaMoO4,  pateraite,  CoMoO4, 
and  belonesite,  MgMoO4. 

ECONOMIC   IMPORTANCE. 

The  only  ores  are  molybdenite  and,  in  one  or  two  instances, 
wulfenite.  The  production  is  chiefly  from  Queensland  and  New 
South  Wales,  Australia,  South  Norway  and  Canada.  The  pro- 
duction probably  is  not  over  300  tons  per  year.f  None  was 
produced  in  this  country  in  1914-1915,  though  work  was  com- 
menced on  a  deposit  near  Georgetown,  Colo.  In  general,  the  ore 
is  less  than  3  per  cent,  and  is  concentrated  by  flotation. 

An  alloy  with  iron  or  manganese  containing  50  to  75  per  cent. 
Mo,  is  prepared  by  the  alumino-thermic  process  or  by  heating  the 
molybdenite  in  a  carbon  tube  with  the  electric  arc,  and  is  used  to 
toughen  and  harden  steel  for  wire  drawing,  tool  steel,  crank  and 
shaft  forgings,  etc.  Alloys  with  nickel  and  chromium  are  also  made. 

The  metal  is  used  in  various  electrical  devices. 

A  considerable  quantity  is  used  in  the  production  of  molyb- 
denum salts,  such  as 

Ammonium  molybdate,  used  to  determine  phosphorus  in  iron 

*  Silicates  are  unknown, 
f  Australia,  1913,  145  tons. 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.      349 

and  in  Europe  as  a  fireproofing  material  and  as  a  disinfectant. 
Sodium  molybdate,  used  to  impart  a  blue  color  to  pottery  and  in 
dyeing  silks  and  woolens,  and  molybdic  acid  from  which  useful 
chemical  reagents  are  prepared. 

The  great  demand  from  France  in  1914  is  said  to  be  due  to  a 
process  for  the  preservation  of  cordite.* 

FORMATION   AND    OCCURRENCE    OF    MOLYBDENUM    DEPOSITS. 

Molybdenum  occurs  in  igneous,  metamorphic  and  sedimentary 
rocks,  principally  as  the  sulphide  molybdenite. 

The  economically  important  deposits  appear  to  be  always  con- 
nected with  granites  and  frequently  associated  with  tungsten. 

Disseminated — or  following  joints  and  crevices  as  at  Cooper, 
Maine. 

In  pegmatites — as  at  Romaine,  Quebec. 

In  veins  in  granite — as  at  Knaben  Mine,  S.  Norway;  Chelan 
county,  Washington;  and  Dillon,  Montana. 

Contacts. — Sometimes  in  contacts  of  granite  with  limestone,  as 
at  Texeda  Island,  B.  C.,  where  the  molybdenite  is  fine-grained 
and  massive  and  included  in  ore  bodies  of  bornite  and  chalcopyrite. 

MOLYBDENITE. 

COMPOSITION.— MoS2,    (Mo  60.0,  S  40.0  per  cent.). 

GENERAL  DESCRIPTION. — Thin  graphite-like  scales  or  foliated 
masses  of  metallic  lustre  and  bluish  gray  color,  easily  separated 
into  flexible  non-elastic  scales.  Sometimes  in  tabular  hexagonal 
forms  and  fine  granular  masses.  Soft,  unctuous  and  marks  paper. 

Physical  Characters.     H.,  I  to  1.5.     Sp.  gr.,  4.6  to  4.9. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  greenish.*  TENACITY,  sectile  to  malleable. 

COLOR,  bluish  lead  gray.  CLEAVAGE,  basal. 

BEFORE  BLOWPIPE,  ETC. — In  forceps  infusible,  but  at  high  heat 
colors  the  flame  yellowish  green.  On  charcoal  gives  sulphurous 
odor  and  slight  sublimate,  yellow  hot,  white  cold,  and  deep  blue 
when  flashed  with  the  reducing  flame.  Soluble  in  strong  nitric 
acid  and  during  solution  on  platinum  it  is  luminous.  With  sul- 

*  Mineral  Industry,  1914,  p.  529. 


350  MINERALOGY. 

phuric  acid  yields  a  blue  solution.     In  salt  of  phosphorous  and 
borax  yields  characteristic  molybdenum  reactions. 

SIMILAR  SPECIES. — Differs  from  graphite  in  streak  and  blowpipe 
reactions.  May  usually  be  distinguished  by  its  lighter  bluish  gray 
color. 

REMARKS. — Economic  deposits  are  as  stated,  p.  349.  Commercially  unimportant 
occurrences  are  in  the  tin  mines  of  Bohemia,  Saxony,  Cornwall  and  elsewhere  and 
the  minute  flakes  common  in  California  gold  quartz  and  the  copper  veins  of  Clifton, 
Arizona,  and  Chili.  It  is  found  in  many  American  localities,  especially,  Westmore- 
land, N.  H.,  Blue  Hill  Bay,  Maine,  Okanogan  Co.,  Wash.,  and  Pitkin,  Colorado. 

MOLYBDITE. 

COMPOSITION. — MoOs,  (Mo  66.7  per  cent.).f 

GENERAL  DESCRIPTION. — An  earthy  yellow  powder  or,  rarely  tufts  and  hair-like 
crystals  of  yellowish-white  color. 

PHYSICAL  CHARACTERS. — Opaque  to  translucent.  Lustre,  dull  or  silky.  Color, 
yellow  or  yellowish  white.  Streak,  straw  yellow.  H.,  i  to  2.  Sp.  gr.,  4.49  to  4.5. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses,  yielding  crystals  yellow  hot,  white 
cold,  and  made  deep  blue  by  the  reducing  flame.  In  borax  and  salt  of  phosphorus 
gives  characteristic  molybdenum  reactions. 

WULFENITE. 

COMPOSITION. — PbMoO4,  sometimes  containing  Ca,  Cr.  V. 

GENERAL  DESCRIPTION. — Usually  in  thin,  square,  tetragonal 
crystals  of  yellow,  orange  or  bright  orange-red  color  and  resinous 
lustre.  Less  frequently  in  granular  masses  or  acute  pyramidal 
crystals.  H.,  3.  Sp.  gr.,  6.7-7. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  on  charcoal,  giving  yel- 
low coat  and  finally  a  metallic  globule. 

Tests  with  sulphuric  acid,  borax  and  salt  of  phosphorus  as 
described,  p.  190. 

REMARKS. — Wulfenite  occurs  with  other  lead  minerals.  It  is  found  in  many 
localities  in  New  Mexico  and  Arizona  ;t  in  the  lead  regions  of  Wisconsin  and 
Arizona;  at  Phcenixville,  Pa.;  Inyo  County,  Cal.;  Southampton,  Mass.,  and  many 
other  places,  always  associated  with  other  ores  of  lead. 

THE  TUNGSTEN   MINERALS. 

The  minerals  described  are: 

Wolframite  (FeMn)WO4  Monoclinic 

Scheelite  CaWO4  Tetragonal 

*  Best  seen  on  glazed  porcelain. 

t  According  to  Schaller  it  is  molybdate  of  iron.     Zeit.  f.  Kryst.,  43,  331. 

\  Commercial  quantities  have  been  obtained  from  the  Mammoth  Mine,  Pinal  Co. 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.      351 

Minor   species  are  tungstite,  meymacite,  cuprotungstite,  cupro- 
scheelite  and  stolzite. 

ECONOMIC   IMPORTANCE. 

The  world's  total  production  is  about  10,000  tons  per  year  of 
60  per  cent.  WO3.  In  1915  the  United  States  produced  2,165  tons 
chiefly  from  Colorado  and  California.  The  great  producers  in 
1913  were:* 

Burma i,732         Australia 752 

United  States 1,397         Bolivia 564 

Portugal 1,380        Argentina 539 

The  material  is  often  recovered  as  a  by-product  from  tin,  as  at 
Heberton,  Queensland,  or  in  the  treatment  of  gold  or  silver  ores 
(British  Columbia)  or  with  copper  ores  (Peru)  and  usually  under- 
goes preliminary  concentration  (to  60  per  cent.  WO3). 

Tungstic  oxide,  WO3,  may  first  be  extracted  from  the  ore  and 
this  reduced  to  tungsten  in  the  powder  form. 

In  this  country  the  ore  is  reduced  directly  in  the  electric  furnace 
to  ferro-tungsten,  which,  added  to  steel,  gives  a  product  of  great 
toughness,  especially  valued  for  high-speed  cutting  tools,  which 
retain  their  temper  even  when  red  hot  and  are  said  to  save  20  to 
30  per  cent,  in  power  alone.  The  steel  is  also  used  for  armor  plate 
and  projectiles  and  for  permanent  magnets.  Alloys  with  Pt,  Cr, 
Co,  Al,  etc.,  are  made,  the  tungsten  usually  giving  strength  to  the 
alloy. 

Metallic  tungsten  is  used  in  place  of  platinum  for  winding  resis- 
tance furnaces  and  in  electrical  contacts  and  as  a  filament  in 
incandescent  lamps.  Its  melting  point  is  3267°  C. 

Tungstic  acid  and  sodium  tungstate  are  used  in  dyeing  and  to 
render  cotton  and  wood  uninflammable.  Other  uses  are  in  pig- 
ments. 

THE   FORMATION   AND    OCCURRENCE   OF   TUNGSTEN    DEPOSITS. 

Veins. 

The  only  important  ores  are  wolframite  and  scheelite,  these 
occur  chiefly  in  veins  in  or  near  granite  either  with  cassiterite  or 
of  the  cassiterite  type,  but  also  in  veins  with  silver,  gold,  etc. 

*  Mineral  Industry,  1914,  p.  756. 


352  MINERAL  OGY. 

Veins  with  Cassiterite. — Wolframite  is  the  most  constant  asso- 
ciate of  cassiterite  and  secondary  scheelite  is  frequent.  Examples 
are: 

Tavoy  District,  Lower  Burma;  tungstite  said  also  to  occur. 
Sierra  de  Estrella,  Portugal;  with  much  arsenopyrite. 
Heberton,  Queensland;  Cornwall;  Zinnwald  and  Altenbefg. 

Veins  without  Cassiterite. — 

Wolframite  occurs  at  Sierra  de  Cordoba,  Argentina  (carries 
Columbium);  Castello  Branco,  and  Beira,  Portugal;  Boulder 
county,  Colorado,  near  silver  and  gold  veins.  In  some  of  the 
Queensland  and  Chilean  veins  it  is  intimately  associated  with 
bismuth  or  silver. 

Scheelite  often  occurs  in  gold  veins  as  in  Atolia,  Kern  county, 
California;  Halifax  county,  Nova  Scotia;  in  veins  in  slate  with 
gold-bearing  arsenopyrite,  and  Sloan  District,  British  Columbia, 
in  large  lenses.  Large  deposits  exist  at  Scheelite,  Nevada. 

Replacements. 

The  deposits  at  Trumbull,  Conn.,  are  regarded  as  replacements* 
of  limestone;  the  scheelite  preceded  the  wolframite,  the  latter 
occurring  only  as  pseudomorphs  after  scheelite.  The  deposits 
near  Lead  and  Dead  wood,  South  Dakota,  are  in  dolomite. 

WOLFRAMITE,   Ferberite,   Huebnerite. 

COMPOSITION. — (Fe.Mn)WO4.  (About  76  per  cent.  WO3.) 
Strictly  Fe\VO4  is  ferberite,  MnW04  is  huebnerite.  The  species, 
however,  replace  each  other.f 

GENERAL  DESCRIPTION. — Heavy  dark-gray  to  black  sub- 
metallic  crystals,  orthorhombic  in  appearance,  bladed  non-termi- 
nated crystals  often  reddish  brown  in  color,  cleavable  and  granular 
masses. 

CRYSTALLIZATION. — Monoclinic.         Axes  a  :  b  :  c  =  0.830  :  i 
0.868,  ft  =  89°  22'. 

Usual  combination  shown  in  Fig.  378  of  unit  prism  m,  ortho 

*  Beck  and  Weed,  p.  539. 

f  F.  L.  Hess  proposes  the  arbitrary  distinction  into  ferberite  for  iron  tungstate 
with  less  than  20  per  cent,  manganese  tungstate,  huebnerite  for  manganese  tungstate 
with  less  than  20  per  cent,  iron  tungstate  and  wolframite  for  all  intermediate  pro- 
portions. 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.       353 


pinacoid    a, 

e  =  (a 
=  81° 


unit  clino  dome    d    and    +    and    — 
102}  Supplement  angles,  mm 
ae  =  62° 


QO  b  :  Ytf}', 
ae  =  61° 


ortho  domes 
=  79°  23';  dd 


FIG.  378. 


Zinnwald. 


54;  ae  =     1    54;  ae  =    2    54. 
Physical  Characters.  —  H.,  5  to  5.5.     Sp.  gr.,  6.8 

to  7-55- 

LUSTRE,  resinous  to  sub-metallic. 

STREAK,    dark-brown,    yellowish-brown    and 
gray. 

COLOR,  dark-gray,  black,  and  reddish-brown. 

OPAQUE    to    translucent.       In    one    locality 
transparent. 

CLEAVAGE  very  perfect  in  one  direction,  joio). 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  readily  to  a  crystalline  globule, 
which  is  magnetic.  In  salt  of  phosphorus  yields  a  reddish-yellow 
glass,  which  in  reducing  flame  becomes  green,  and  if  this  bead  is 
pulverized  and  dissolved  with  tin,  in  dilute  hydrochloric  acid,  a 
blue  solution  results. 

Partially  soluble  in  hydrochloric  acid,  the  solution  becoming 
blue  on  addition  of  tin. 

SIMILAR  SPECIES.  —  Distinguished  by  its  fusibility  and  specific 
gravity  from  similar  iron  and  manganese  minerals. 

REMARKS.  —  The  chief  occurrences  are  as  stated,  p.  352,  and  other  similar  deposits 
in  Angaras,  Peru;  Siam;  Salamanca,  Spain;  St.  Leonards,  France;  Brazil  and  else- 
where. Found  also  in  many  deposits  of  stream  tin,  sometimes  in  considerable 
quantities.  Occurs  in  at  least  twelve  of  the  United  States,  but  is  worked  chiefly  in 
Colorado,  and  to  a  minor  extent  in  Idaho,  Nevada,  New  Mexico  and  South  Dakota. 

SCHEELITE. 

COMPOSITION.—  CaWO4,  (CaO  19.4,  WO3  80.6  per  cent.),  some- 
times with  replacement  by  molybdenum. 

GENERAL  DESCRIPTION.  —  Heavy  brownish  white  or  white 
masses  and  square  pyramids.  Also  drusy  crusts  of  yellow  or 
brown  crystals. 

CRYSTALLIZATION.  —  Tetragonal.  Class  of  third  order  pyramid, 
p.  47.  Axisc  =  1.536. 

The  unit  first  order  pyramid  p  and  second  order  d  are  most 
common  with  sometimes  a  modifying  third  order  pyramid,  x  =  (a  : 
3a  :3C)>    !3n)-     Supplement  angles  are  pp  =  79°  55';  ee  =  72° 
40'. 
24 


354 


FIG.  379. 


MINERALOGY. 
FIG.  380. 


FIG.  381. 


Schlackenwald. 


Trumbull,  Conn. 


Physical  Characters.     H.,  4.5  to  5.     Sp.  gr.,  54  to  6.1. 

LUSTRE,  adamantine.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  pale  yellow,  gray,  brown,  white  or  green. 

CLEAVAGE,  distinct  parallel  to  first  order  pyramid,  indistinct 
parallel  to  second  order  pyramid. 

BEFORE  BLOWPIPE,  ETC. — Fusible  with  difficulty  on  sharp  edges. 
In  salt  of  phosphorus  forms  a  clear  bead  which  in  the  reducing 
flame  becomes  deep  blue,  and  if  the  bead  is  powdered  and  dis- 
solved in  dilute  hydrochloric  acid  it  yields  a  deep  blue  solution, 
especially  on  addition  of  metallic  tin.  Scheelite  is  soluble  in  hy- 
drochloric or  nitric  acid,  leaving  a  yellow  residue. 

SIMILAR  SPECIES. — Distinguished  among  non-metallic  minerals 
by  its  weight  and  behavior  in  salt  of  phosphorus. 

REMARKS. — The  chief  occurrences  are  as  stated,  p.  352;  it  is  also  frequent  as  a 
secondary  mineral  with  wolframite.  There  are  many  minor  occurrences  with  gold 
or  silver  or  lead  and  copper  deposits.  Examples  are  with  gold  at  Warren's,  Idaho,  and 
Val  Toppa,  Piedmont,  with  silver  and  lead  at  Oracle,  Arizona,  and  Snake  River, 
Nevada;  with  copper  at  Llamuco,  Chile. 

THE    COLUMBIUM    AND    TANTALUM    MINERALS. 

The  minerals  described  are': 


Columbite  1 
Tantalite    j 
Samarskite 
Fergusonite 


(Fe.Mn)(CbTa)2O6  Orthorhombic 

(Fe.Ca.U02)3(Y.Er.Ce)2(Cb.Ta)602i      Orthorhombic 
(YEr.Ce)(Cb.Ta)O4  Tetragonal 


Less  common  are  yttrotantalite,  pyrochlore,  euxenite,  skogbolite, 
stibiotantalite. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     355 

The  wolframites  of  Rosario,  Argentina;  and  Auvergne,  France, 
contain  columbium. 

ECONOMIC   IMPORTANCE. 

No  production  is  reported  for  this  country,  the  small  amount 
used,  possibly  100  tons,  coming  from  Western  Australia.  Colum- 
bium has  practically  no  uses ,  tantalum,  on  account  of  its  hardness, 
toughness,  ductility  and  high  fusion  point  (2,250°  to  2,300°  C.) 
is  made*  into  filaments  for  incandescent  lights  which  are  con- 
siderably used. 

It  is  used  in  dental  and  surgical  steel,  watch  springs,  etc.,  and 
is  suggested  for  laboratory  crucibles. 

FORMATION    AND    OCCURRENCE    OF    COLUMBIUM    AND    TANTALUM 

DEPOSITS. 

These  elements  are  usually  found  together  and  the  minerals 
which  they  form  are  found  almost  entirely  in  granite  pegmatites, 
as  at  the  Etta  Mine,  South  Dakota,  or  in  the  gravels  resulting 
from  the  decomposition  of  pegmatites  as  at  Greenbushes,,  West 
Australia,  in  pebbles  5-6  inches  in  diameter.f 

COLUMBITE.—  TANTALITE. 

COMPOSITION. — (Fe,  Mn)(Cb,  Ta)2O6  (grading  from  columbite, 
FeCb2O6,  to  tantalite,  FeTa2Oe).  Usually  contains  a  little  tin, 
often  a  little  tungsten. 

GENERAL  DESCRIPTION. — Black,  often  bright  and  sometimes 
iridescent  crystals.  Also  in  large  dull  black  masses  and  in  pebbles 
in  tin  gravels. 

CRYSTALLIZATION. — Orthorhombic.     a  :  b  :  c  =  .828  :  I  :  .889. 
Common    forms  a  {oioj,  b  }iooj,    m  =  {no},  d  {739}.     Supple- 
ment angle  mm  =  79°  17'. 
Physical  Characters. — H.>  6.     Sp.  gr.  5.4  to  7. 

LUSTRE,  sub-metallic.  OPAQUE. 

STREAK,  dark  red  to  black.  TENACITY,  brittle. 

COLOR,  black. 

CLEAVAGE  in  two  directions  at  right  angles. 

*  By  pressing  a  mixture  of  the  oxide  and  paraffine  into  threads,  then  reducing 
them  to  metal  in  a  vacuum.  It  is  said  one  pound  of  tantalum  will  make  20,000 
2o-candle  power  filaments. 

t  Also  small,  dull  pebbles  of  stibiotantalite,  Sb  (CbTa)2O8. 


356 


MINERALOGY. 


BEFORE  BLOWPIPE,  ETC. — Infusible.  Fused  with  potassium 
hydroxide  and  boiled  with  tin  gives  deep-blue  solution  on  dilution 
with  water  the  color  disappears.  Insoluble  in  hydrochloric  acid, 
partially  decomposed  by  sulphuric  acid. 

SIMILAR  SPECIES. — By  infusibility  and  lower  specific  gravity 
from  wolframite,  by  greater  opacity  and  absence  of  tin  test  from 
cassiterite. 

REMARKS. — Occurs  in  considerable  quantities  in  large  black  crystals  at  the  Etta 
Mine,  Black  Hills,  South  Dakota,  and  as  pebbles  5-6  inches  in  diameter  in  the  tin 
gravels  of  Greenbushes,  Western  Australia. 

Famous  crystal  localities  are  the  cryolite  of  Greenland,  the  granites  of  Bodenmais, 
Bavaria;  Miask,  Urals;  Haddam,  Connecticut  and  Amelia  Co.,  Virginia.  It  is 
found  in  the  gold  sands  of  Sanarka  Urals. 

FIG.  384. 


FIG.  382. 


FIG.  383. 


Coiumbite. 


Samarskite. 


Fergusonite. 


SAMARSKITE. 

COMPOSITION.— RsR2(Cb,Ta)6O2i.    R  chiefly  FeCaUO2.    RCe,  Yt  metals. 

GENERAL  DESCRIPTION. — Irregularly  shaped  masses  and  rough  orthorhombic 
crystals  (Fig.  383)  of  velvet  black  color  and  notable  lustre.  Streak  reddish  brown. 
H.,  5  to  6.  Sp.  gr.,  5.6  to  5-8. 

BEFORE  BLOWPIPE,  ETC. — Fuses  with  difficulty  to  black  glass;  in  closed  tube 
glows,  cracks  and  blackens.  With  salt  of  phosphorus  green  uranium  bead.  De- 
composed sufficiently  by  boiling  concentrated  sulphuric  acid  to  give  a  blue  color  on 
addition  of  zinc  or  tin  and  hydrochloric  acid. 

REMARKS. — Found  in  granite  pegmatites  at  Mitchell  and  McDowell  counties, 
North  Carolina,  and  near  Miask,  Urals,  in  both  cases  with  columbite.  Also  in 
Queensland,  Australia. 

FERGUSONITE. 

COMPOSITION.— (Y,  Er,  Ce)(CbTa)O4. 

GENERAL  DESCRIPTION. — Brownish  black,  tetragonal  crystals  (Fig.  384)  and 
masses  with  brilliant  glassy  lustre  on  fresh  fracture.  Streak  pale  brown.  H.,  5.5  to 
6.  Sp.  gr.,  5.8  or  less  if  hydrated. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  becomes  pale  yellow  on  charcoal.  De- 
composed by  sulphuric  acid,  the  white  residue  giving  a  blue  color  with  tin  and 
hydrochloric  acid. 


MINERALS   OF  METALLIFEROUS    ORE  DEPOSITS.     357 


Copper 

Cu 

Isometric 

Covellite 

CuS 

Hexagonal 

Chalcocite 

Cu2S 

Orthorhombic 

Bornite 

Cu5FeS4 

Isometric 

Chalcopyrite 

CuFeS2 

Tetragonal 

Enargite 

Cu3AsS4 

Orthorhombic 

Famatinite 

Cu3SbS4 

Tetrahedrite 

CusSbizS; 

Isometric 

Cuprite 

Cu20 

Isometric 

Tenorite 

CuO 

Triclinic 

Atacamite 

Cu(OH)Cl.Cu(OH)2 

Orthorhombic 

Chalcanthite 

CuSO4.5H20 

Triclinic 

Brochantite 

Cu4SO4(OH)6 

Orthorhombic 

Malachite 

Cu2(OH)2C03 

Monoclinic 

Azurite 

Cu3(OH)2(C08)2 

Monoclinic 

Chrysocolla 

£uSiO3.2H2O 

REMARKS. — Occurs  in  considerable  quantity  in  the  granite  of  Baringer  Hill, 
Llano  Co.,  Texas.  Other  localities  are  Cape  Farewell,  Greenland;  Ytterby,  Sweden; 
Arendal,  Norway. 

THE   COPPER   MINERALS. 

The  minerals  described  are : 

Metal 
Sulphides 


Sulphoarsenite 

Sulphoantimonite 
Oxides 

Basic  chloride 
Sulphates 

Carbonates 
Silicates 

The  great  deposits  of  pyrite  and  pyrrhotite  usually  carry  copper 
and  both  directly  because  of  its  extraction  and  indirectly  as  the 
primary  ores  from  which  the  richer  ores  largely  form  are  the 
greatest  and  most  important  sources. 

ECONOMIC   IMPORTANCE. 

The  world's  production  of  copper  in  1915  was  1,061,283  metric 
tons,  of  which  this  country  produced  646,212;  Bolivia,  75,000; 
Canada  47,202;  Peru,  47,142;  and  Mexico,  Australia,  Germany,, 
Africa,  Spain  and  Portugal  from  25,000  to  35,000  each. 

The  ores  which  yielded  this  product  probably  do  not  differ 
greatly  in  proportions  from  an  earlier  estimate, f  based  on  the 
production  of  1909. 

Sulphide  ores 60  to  65  per  cent. 

Oxidized  ores 15  to  20         " 

Native  copper 12  " 

Enargite 5 

Tetrahedrite Y^ 

The  production  in  this  country  was  derived  approximately  in 
the  following  percentages :  Arizona,  31;  Montana,  18.5;  Michigan, 

*  Engineering  and  Mining  Journal,  1916,  p.  48. 
t  Beyschlag,  Vogt  &  Krusch  (Truscott),  872. 


358  MINERALOGY. 

17;  Utah,  13;  New  Mexico,  4.5;  Nevada,  4;  Alaska,  4;  the  re- 
maining 8  per  cent,  chiefly  from  California,  Idaho  and  Tennessee. 

The  method  of  extraction  of  the  copper  is  dependent  upon  the 
nature  of  the  ore,  and  may  roughly  be  classed  under  three  headings : 

Treatment  of  native  copper. 

Treatment  of  oxidized  ores. 

Treatment  of  sulphides. 

A  great  many  processes  exist  or  have  existed,  but  these  for  a 
general  brief  discussion  may  be  reduced  to  a  small  number  of  type 
processes  of  which  the  others  are  variations  due  to  local  conditions 
or  constituents  of  the  ore. 

Treatment  of  Native  Copper. 

Native  copper  occurs  in  enormous  quantities  in  Michigan,  and 
the  deposits  mined  average  less  than  two  per  cent,  of  copper,  al- 
though occasionally  large  masses  of  the  metal  are  found.  The 
rock  is  crushed  by  steam  stamps  and  the  copper  separated  from 
the  rock  by  the  action  of  water  and  the  use  of  jigs,  tables,  and  other 
concentrating  apparatus.  The  concentrated  material  is  then  melted 
in  a  large  reverberatory  furnace  with  limestone  and  slags  from  previ- 
ous operations.  The  new  slag  thus  formed  contains  the  remain- 
ing rock  and  is  removed,  leaving  behind  copper,  which  after  a 
period  of  reduction  by  charcoal  and  stirring  is  cast  into  ingots. 

Treatment  of  Oxidized  Ores. 

The  oxidized  ores  in  Arizona  which  averaged  over  ten  per  cent, 
of  copper,  were  smelted  in  blast-furnaces  with  coke  and  the  neces- 
sary flux  to  make  a  slag  with  the  associated  gangue.  The  result 
being  an  impure  metal  called  black  copper,  which  was  later  refined. 
The  ores  are  now  more  often  mixed  with  sulphides. 

The  carbonate  and  silicate  ores  at  Ajo,f  Arizona,  carrying  1.5 
per  cent,   copper,  are  being  leached  with  dilute  sulphuric  acid 
and  electrolytically  precipitated. 
Treatment  of  Sulphides. 

The  treatment  of  sulphides  is  quite  varied,  depending  chiefly  on 
the  precence  or  absence  of  arsenic,  the  richness  of  the  ore  and  the 
local  conditions. 

*  Engineering  and  Mining  Journal,  1916,  p.  48. 
t  Ibid.,  p.  55- 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.     359 

The  modern  practice  involves  a  concentration  by  flotation  which 
may  bring  a  2  per  cent,  ore  up  to  25  per  cent.,  but  makes  necessary, 
on  account  of  the  pulverized  condition,  either  a  roasting  or  smelting 
in  a  reverberatory  furnace  or  sintering  and  then  smelting  in  a  blast 
furnace.* 

The  ores  always  contain  iron,  copper  and  sulphur,  and  may  contain  arsenic, 
antimony,  silver,  gold,  etc.  All  the  smelting  processes  depend  on  the  facts  that  at 
high  temperatures  copper  has  a  greater  affinity  for  sulphur  than  iron  has,  and  iron 
a  stronger  affinity  than  copper  for  oxygen.  So  that  if  such  an  ore  is  subjected  to 
oxidation  by  roasting,  oxides  result;  but  in  the  subsequent  fusion,  if  enough  sulphur 
has  been  left,  the  copper  will  form  a  fusible  sulphide,  and  the  oxidized  iron  will  unite 
with  the  gangue  and  the  flux  to  form  a  slag. 

By  regulating  the  roasting,  the  sulphur  contents  may  be  brought  to  any  desired 
percentage. 

The  roasted  ore  is  smelted  for  copper  either  in  a  shaft-furnace,  or 
when  silver  or  gold  is  present,  in  a  reverberatory  furnace.  The 
blast  furnaces  are  rectangular  in  cross  section  and  may  be  as  large 
as  25  ft.  x  144  ft.  and  may  treat  over  3,000  tons  per  day. 

The  slag  and  matte  flow  through  a  trapped  spout  to  an  outer 
fore  hearth  where  the  matte  settles  and  is  tapped  and  the  slag 
flows  out  at  the  top. 

The  copper  matte  is  often  blown  in  a  converter,  by  which  the 
sulphur,  arsenic  and  antimony  are  driven  off,  the  iron  oxidized 
and  converted  into  slag,  and  black  copper  obtained. 

The  crude  copper  is  refined  either  by  remelting  and  oxidation, 
or  more  frequently  electrolytically. 

The  great  uses  of  copper  are  in  electrical  work  and  in  alloys 
with  zinc  and  tin,  such  as  brass,  yellow  metal,  bronze,  bell  metal, 
and  German  silver.  Copper  sulphate  is  also  important. 

THE  FORMATION  AND  OCCURRENCE  OF  COPPER  ORES. 

Copper  is  obtained  from  deposits  of  all  the  great  classes  and  it 
is  estimated f  that  the  world's  yield  is  about  in  the  following 
proportions : 

Magmatic  segregation 10  to  n  per  cent. 

Contacts  and  contacts  combined  with  veins 25  to  30         " 

Veins 40          " 

Metasomatic  replacements 3 

Native  copper 12         " 

Ore  beds 4 

By-products I 

*  Lawrence  Addicks  in  Eng.  and  Min.  Journ.,  1916,  p.  91. 
t  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  944. 


360  MINER ALOG  Y. 

Magmatic  Segregations. 

The  chalcopyrite  in  norite  at  Sudbury,  the  sulphides  in  serpen- 
tine at  Mt.  Catini,  Tuscany,  and  the  bornite  at  O'kiep  Namaqua- 
land,  Cape  Colony,  in  a  rock  chiefly  feldspar,  are  generally  accepted 
as  segregations. 

Many  bedded  copper  deposits  formerly  attributed  to  heated 
waters  are  probably  magmatic  intrusions  such  as  the  great  copper- 
bearing  pyrite  deposits  of  Rio  Tinto,  Spain,  and  Mt.  Lyell, 
Tasmania.* 

Contacts  Usually  with  Veins. 

True  contacts  with  garnet,  augite,  wernerite,  wollastonite, 
vesuvianite,  etc.,  are  often  associated  with  ordinary  copper  veins- 

The  great  deposits  of  this  type  are:  Clifton,  Bisbee,  and  Globe, 
Arizona;  Mednorudiansk,  Urals;  Bingham  Canon,  Utah;  and 
Cananea,  Mexico. 

Veins. 

This  most  productive  class  includes  the  great  deposits  of  chalco- 
cite,  bornite  and  enargite  at  Butte,  Montana,  in  granite  near 
rhyolite;  Burra  Burra,  S.  Australia,  of  carbonates  and  oxides,  in  a 
complex  of  slate,  limestone  and  sandstone;  Moonta  and  Wallaroo, 
S.  Australia,  of  chalcopyrite  and  bornite  in  quartz  porphyry  but 
with  the  carbonates  and  atacamite  in  large  quantities;  Aschio 
Japan.  Sometimes  the  presence  of  tourmaline  or  cassiterite  indi- 
cate high  temperatures  and  cooperation  of  vapors  as  at  Cactus 
Mine,  Utah;  Las  Condes,  Chili;  Dolceath  Mine,  Cornwall;  Heber- 
ton,  Australia. 

Metasomatic  Replacements. 

The  great  auriferous  pyrite  deposits  of  Rio  Tinto  and  Mt.  Lyell 
mentioned  under  magmatic  segregations  are  by  some  regarded 
as  replacements. f 

The  copper-bearing  pyrrhotite  and  pyrite  of  Ducktown,  Tenn., 
are  said  to  have  been  formed  by  replacement  of  limestone  by 
"igneous  emanations. "§ 

*  Ibid.,  943  and  877. 
t  Lindgren,  p.  602,  605. 
t  Ibid.,  p.  709. 


MINERALS   OF  METALLIFEROUS    ORE  DEPOSITS.     361 

Other  replacements  are  the  important  deposits  of  Bosccheggrano, 
Tuscany,  and  Otavi,  German  S.  W.  Africa.* 

Sedimentary. 

Occurrence  in  beds  in  sedimentary  rocks  does  not  prove  sedi- 
mentary origin. 

Throughout  Europe  and  America  sandstones  are  found  which 
contain  copper  ores,  chiefly  chalcocite,  but  of  date  later  than  the 
sediments  and  probably  deposited  from  solutions  of  pre-existing 
ore  in  the  sediments  or  adjoining  rocks.  Such  deposits  occur  at 
Coro  Coro,  Bolivia;  Colorado  and  New  Mexico;  the  Permian 
sandstones  of  Russia,  and  elsewhere. 

At  Boleo,  Lower  California,  conglomerates  and  tuffs  interstrati- 
fied  with  copper  minerals  occur,  the  tuffs  being  regarded  as  intru- 
sions of  volcanic  mud  and  the  concentration  of  the  copper  minerals 
to  the  action  of  springs.  Nodules  of  malachite  and  azurite  occur 
in  the  Bunter  sandstone  in  many  localities, \  some  of  which  are 
worked,  as  in  Lorraine;  Rhenish  Prussia;  Mottram,  St.  Andrews, 
England;  etc. 

Copper  is  sometimes  found  in  placers  and  river  beds  as  at  Ste. 
Catalina,  Argentina. 

Native  Copper  in  Basic  Lava  Flows. 

The  one  great  occurrence  is  in  the  melaphyre  of  the  Lake 
Superior  region,  where  the  copper  occurs  with  zeolites  filling  the 
blowholes  of  the  melaphyre  and  also  the  interstices  in  a  con- 
glomerate, chiefly  melaphyre. 

True  veins  also  occur,  which  are  richest  where  they  cross  the 
melaphyre. 

The  intimate  association  with  calcite  and  the  zeolites  laumontite, 
analcite,  natrolite,  etc.,  and  such  species  as  prehnite,  epidote, 
datolite  (carrying  boron)  and  apophyllite  (carrying  fluorine)  indi- 
cate deposition  from  water  at  moderate  temperatures.  It  is  a 
special  case  of  formation  of  zeolites  differing  from  the  ordinary  only 
in  the  presence  of  copper  in  the  solutions. § 

*  Beyschlag,  Vogt  &  Krusch  (Truscott),  916. 
t  Ibid.,  1182. 
J  Ibid.,  1184. 

§  These  solutions  are  considered  to  be  in  part  of  magmatic  origin  and  to  have  risen 
at  the  consolidation  of  the  rocks.  Beyschlag,  Vogt  &  Krusch  (Truscott),  935. 


362 


MINERALOGY. 


Many  other  relatively  unimportant  occurrences  of  native  copper 
are  associated  with  basic  eruptive  rocks  with  the  same  mineral 
association,  calcite,  prehnite,  epidote  and  zeolites,  such  as  the 
Faroe  Islands;  Oberstein,  Germany;  Bay  of  Fundy,  N.  S. 

Oxidation  and  Cementation,  or    Secondary  Enrichment  of 
Copper    Ores. 

In  the  upper  portions  of  many  copper  deposits  the  primary  ores, 
pyrite,  pyrrhotite,  chalcopyrite,  etc.,  are  oxidized.  If  much  pyrite 
is  present  soluble  sulphates,  CuSO4  and  Fe2(SO<i)3  and  insoluble 
ferric  oxides  and  hydrates  result*  and  the  copper  is  carried  as 
copper  sulphate  by  superficial  waters  to  a  lower  level,  sometimes 
leaving  no  copper  at  the  outcrop  as  at  Butte  and  Rio  Tinto. 
The  copper  from  these  solutions  is  precipitated  both  by  other 
sulphides  and  by  organic  matter  as  chalcocite  or  sometimes  covel- 
lite  or,  if  the  primary  ore  is  pyrite,  partly  as  chalcopyrite,  thus 
forming  a  zone  of  very  much  richer  ore  between  the  leached-out 
gossan  and  the  unchanged  primary  ores  at  greater  depths.  Promi- 
nent examples  of  this  are  found  at  Rio  Tinto,  Spain;  Butte,  Mon- 
tana; Ducktown,  Tennessee;  and  Clifton,  Arizona. 

In  other  cases  in  which  the  primary  ore  is  purer  chalcopyrite  or 
if  carbonates  in  solution  or  as  limestone  neutralize  the  sulphuric 
acid,  rich  deposits  of  oxide  ores  form  near  the  outcrop,  especially 
malachite  and  azurite  as  in  Arizona,  Chessy,  Mednorudiansk, 
Burra  Burra,  or  of  atacamite  as  in  Chili  and  South  Australia. 

COPPER.— Native  Copper. 

COMPOSITION. — Cu  often  containing  Ag,  sometimes  Hg  or  Bi. 
GENERAL  DESCRIPTION.— A  soft,  red,  malleable  metal,  with  a 


FIG.  385. 


FIG.  386. 


FIG.  387. 


*  Beyschlag,  Vogt  &  Krusch  (Truscott),  881. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.      363 

red  streak.  Usually  in  sheets  or  disseminated  masses,  varying 
from  small  grains  to  several  hundred  tons  in  weight.  Also  in 
threads  and  wire  and  in  distorted  crystals  and  twisted  groups. 

CRYSTALLIZATION. — Isometric.  Tetrahexahedron  and  cube 
most  frequent,  Fig.  386,  also  twinned,  Fig.  387,  giving  by  elonga- 
tion spear-shaped  forms  often  complexly  grouped  and  usually 
distorted. 

Physical  Characters.     H.,  2.5  to  3.     Sp.  gr.,  8.8  to  8.9. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  copper  red.  TENACITY,  malleable  and  ductile. 

COLOR,  copper  red,  tarnishing  nearly  black. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  to  a  malleable  globule, 
often  coated  with  a  black  oxide.  In  beads,  becomes  in  O.  F.  green 
when  hot;  blue,  cold,  and  in  R.  F.  opaque  red.  Soluble  in  nitric 
acid,  with  evolution  of  a  brown  gas,  to  a  green  solutio,nwhich  will 
deposit  copper  on  iron  or  steel.  The  solution  becomes  deep  azure 
blue  on  addition  of  ammonia. 

SIMILAR  SPECIES. — Resembles  niccolite  and  tarnished  silver, 
differs  in  copper-red  streak. 

REMARKS. — Occurs  in  basic  lava  flows,  as  described  p.  361,  and  to  a  limited  extent 
in  oxidation  zone  of  other  copper  deposits  as  at  the  Coro  Coro  Mines  in  Bolivia; 
the  Faroe  Islands;  Atacama,  Chili;  Wallaroo,  South  Australia,  and  elsewhere.  In 
this  country  in  addition  to  the  Lake  Superior  deposits  it  has  been  found  in  twenty- 
seven  states. 

COVELLITE.— Indigo  Copper. 

COMPOSITION. — CaS  (Cu  66.44,  S  33-56  per  cent). 

GENERAL  DESCRIPTION.  —Very  dark  indigo  blue  submetallic 
masses  often  purplish  when  moistened.  Rarely  tabular  hexagonal 
crystals.  Streak  shining  gray  to  black.  Somewhat  flexible.  H., 
1.5  to  2.  Sp.  gr.,  4.59  to  4.64. 

BEFORE  BLOWPIPE,  ETC. — Burns  with  blue  flame  and  odor  of 
SO2.  In  closed  tube  a  sublimate  of  sulphur.  Soluble  in  nitric 
acid  and  slowly  soluble  in  hydrochloric  acid. 

REMARKS. — Probably  always  a  cementation  secondary  enrichment  mineral  precipi- 
tated from  copper  sulphate  solutions  by  older  sulphides.  Occurs  in  large  masses  at 
I,ioo  feet  level  of  mines  at  Butte,  Montana.  At  the  Rambler  Mine,  Wyoming,  in- 
cluding the  platinum  mineral  sperrylite.  Foreign  localities  are  Mansfeld,  Thuringia; 
Bolco,  Lower  California;  Chili.  Found  in  various  sandstones  with  chalcocite  as  at 
Cashin  Mine,  Colorado. 


364  MINERAL  OGY. 

CHALCOCITE.— Copper  Glance. 

COMPOSITION. — Cu2S,    (Cu  79.8,  S  20.2  per  cent.). 

GENERAL  DESCRIPTION. — Black  granular  or  compact  masses, 
with  metallic  lustre,  or  sometimes  nodules  or  pseudomorphic  after 
wood.  Often  coated  with  the  green  carbonate,  malachite.  Also 
in  orthorhombic  crystals. 

Physical  Characters.     H.,  2.5  to  3.     Sp.  gr.,  5.5  to  5.8. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  lead  gray.-  TENACITY,  brittle. 

COLOR,  blackish  lead  gray,  with  dull-black  tarnish. 

BEFORE  BLOWPIPE,  Etc. — Yields  no  sublimate  in  closed  tube. 
On  charcoal,  with  soda  in  R.  F.  yields  a  copper  button  and  a 
strong  sulphur  reaction.  If  moistened  with  hydrochloric  acid, 
colors  the  flame  azure  blue.  In  borax  or  salt  of  phosphorus, 
yields  copper  beads.  Soluble  in  nitric  acid,  leaving  a  residue  of 
sulphur> 

SIMILAR  SPECIES. — It  is  more  brittle  than  argentite,  and  differs 
from  bornite  in  not  becoming  magnetic  on  fusion. 

REMARKS. — Often  a  cementation  species  but  also  primary,  as  in  the  deeper  levels 
at  Butte,  Montana,  and  Virgilina,  Va.,  and  the  25  ft.  veins  at  the  Bonanza  Mine, 
Copper  River,  Alaska. 

In  the  numerous  copper  deposits  in  sandstone  the  principal  mineral  is  chalcocite, 
often  replacing  wood  and  plants,  as  in  Texas  and  New  Mexico  and  the  Permian  beds 
of  Russia. 

Famous  localities  for  crystallized  chalcocite  are  Bristol,  Conn.,  and  Cornwall' 
England. 

BORNITE.  —  Purple  Copper  Ore.     Horse  Flesh  Ore. 

COMPOSITION.  —  Cu5FeS4,  (Cu  63.3,  Fe  11.2,  S  25.5  per  cent.), 
but  often  contains  admixed  chalcocite. 

GENERAL  DESCRIPTION. — On  fresh  fracture,  bornite  is  of  a  pecu- 
liar red-brown  color  and  metallic  lustre.  It  tarnishes  to  deep  blue 
and  purple  tints,  often  variegated.  Usually  massive,  sometimes 
small  cubes  or  other  isometric  forms. 

Physical  Characters.     H.,  3.     Sp.  gr.,  4.9  to  54. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  grayish  black.  TENACITY,  brittle. 

COLOR,  dark  copper  red,  brownish  or  violet  blue,  often  varied. 

BEFORE  BLOWPIPE,  ETC.— Blackens,  becomes  red  on  cooling, 
and  finally  fuses  to  a  brittle,  magnetic  globule  and  evolves  sulphur 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.      365 


dioxide  fumes.  In  oxidizing  flame  with  borax  or  salt  of  phosphate 
phorus,  gives  green  bead  when  hot,  greenish  blue  when  cold,  the 
bead  is  opaque  red  in  the  reducing  flame.  Soluble  in  nitric  acid, 
with  separation  of  sulphur. 

REMARKS.  —  Bornite  is  often  found  with  chalcopyrite  and  is  both  primary  and  a 
cementation  product,  as  at  Mt.  Lyell,  Tasmania,  and  Butte,  Montana.  In  certain 
localities  it  is  the  principal  mineral,  as  at  some  Chilian  mines  and  the  magmatic 
segregations  at  O'kiep,  Little  Namaqualand,  Cape  Colony.  It  occurs  also  in  com- 
mercial quantities  with  chalcocite  but  without  chalcopyrite  in  quartz  veins  in  an 
altered  volcanic  rock  at  Virgilina,  Va.,  and  as  lenses  in  limestone  with  little  chalco- 
pyrite on  Texada  Island,  British  Columbia. 

CHALCOPYRITE.—  Copper  Pyrites.    Yellow  Copper  Ore. 

COMPOSITION.  —  CuFeS2,  (Cu  34.5,  Fe  30.5,  S  35.0  per  cent.),  with 
mechanically  intermixed  pyrite  at  times. 

GENERAL  DESCRIPTION.  —  A  bright  brassy  yellow  mineral  of 
metallic  lustre,  often  with  iridescent  tarnish  resembling  that  of 
bornite.  Usually  massive.  Sometimes  in  crystals. 

CRYSTALLIZATION.  —  Tetragonal.  Scalenohedral  class,  p.  47. 
Axis  £  =  0.985. 

Sphenoids    predominate,  /  =  unit    sphenoid  ;  o  =  (a  :  a  :  ^c)  ; 

{772};  t=*(a:a:\c)\  {  1  14}  ;  v  =  (a  :  a  :  4*)  ;  {441};  •*  = 
(a\2a\c)\  {212}. 

Supplement  angles  (over  top)  //  =  108°  40'  ;  00=  128° 


52'  ; 


38°  25' 


159°  39'- 


FIG.  388. 


FIG.  389. 


FIG.  390. 


French  Creek,  Pa. 


Ellenville,  N.  Y. 


Physical  Characters.     H.,  3.5  to  4.     Sp.  gr.,  4.1  to  4.3. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  greenish  black.  TENACITY,  brittle. 

COLOR,  bright  brass  yellow,  often  tarnished  in  blue,  purple  and 
black  hues. 


366  MINER  A  LOG  Y. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  with  scintillation  to 
a  brittle  magnetic  globule.  With  soda  yields  metallic  malleable 
red  button  and  sulphur  test.  In  closed  tube  decrepitates,  becomes 
dark  and  iridescent  and  may  give  deposit  of  sulphur.  Flame  and 
bead  reaction  like  bornite.  Soluble  in  nitric  acid  with  separation 
of  sulphur,  and  from  the  solution  ammonia  throws  down  a  brown 
precipitate,  and  leaves  the  liquid  deep  blue  in  color. 

SIMILAR  SPECIES. — Chalcopyrite  is  softer  and  darker  in  color 
than  pyrite,  and  differs  from  gold  in  black  streak  and  brittleness. 

REMARKS. — Usually  primary,  often  in  small  amount,  cupriferous  pyrite  and  pyr- 
rhotite.  Occurs  also  as  cementation  product,  p.  362.  Occurs  in  all  classes  of 
deposit,  as  described  p.  360,  in  most  of  localities  mentioned  and  in  many  others, 
being  one  of  the  great  sulphides  of  metallic  ore  deposits. 

ENARGITE. 

COMPOSITION.  —  Cu3AsS4,  (Cu  48.3,  As  19.1,  S  32.6  per  cent). 
Sometimes  with  Cu  replaced  in  part  by  Zn  or  Fe  and  As  by  Sb. 
GENERAL  DESCRIPTION. —  A  black  brittle  min- 
FIG.  391.  eraj  Of  metallic  lustre,   occurring  usually  colum- 

nar or   granular  but   sometimes   in    orthorhom- 
bic  crystals. 

CRYSTALLIZATION.  —  Orthorhombic.  Axes  a: 
b  \  c  —  0.871  :  i  :  0.825.  m  =  unit  prism,  /  = 
(2%  \T>  \  cor);  {120}.  Supplement  angles  are 
mm  =  82°  7';  //=  120°  7'. 

Missouia  Co.,  Mont.    Physical  Characters.     H.,  3.     Sp.  gr.,  4.43  to 

4.45. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  blackish  gray.  TENACITY,  brittle. 

COLOR,  black  or  blackish  gray. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses,  yields  white  fumes 
with  garlic-  odor.  With  soda  yields  malleable  copper  and  a  reaction 
for  sulphur.  In  closed  tube  decrepitates,  yields  sulphur  sublimate, 
then  fuses  and  yields  red  sublimate  of  arsenic  sulphide.  Soluble 
in  nitric  acid. 

REMARKS. — As  stated,  p.  357.  enargite  is  one  of  the  great  ores,  yielding  probably  five 
per  cent,  of  the  copper  of  the  world.  It  is  apparently  a  primary  mineral  and  forms 
nearly  one  third  of  the  ore  at  Butte,  Montana.*  Other  large  deposits  are  Sierra 

*  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  871. 


I 
I 

,-»* 


r 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.      367 

Famatina,  Argentina;  in  clay  slate;  Tinctic,  Utah;  with  rich  silver  and  gold  minerals; 
Mancanyan,  Luzon;  with  tetrahedrite  in  porphyry;  Morococha  and  Cerro  de  Pasco, 
Peru,  with  tennantite;  Hedworda  Mine  near  Coquimbo,  Chili,  at  Bor,  Servia  and 
Parad,  Hungary,  in  porphyry. 

FAMATINITE. — CusSbS4  (Cu  43.3;  Sb  27.4;  S  29.3,  per  cent.)  is  a  mineral  of 
metallic  lustre  and  granular  structure  with  a  color  suggesting  that  of  fresh  fractured 
bornite.  Streak  black.  H.,  3  to  4.  Sp.  gr.,  4.5  to  4.6.  Before  the  blowpipe  it 
gives  off  white  fumes  of  antimony  and  leaves  a  brittle  black  globule.  It  is  found  with 
enargite  at  Sierra  Famatina,  Argentina,  and  Cerro  de  Pasco,  Peru,  in  considerable 
quantities.  It  is  associated  with  the  ores  of  Goldfield,  Nevada. 


TETRAHEDRITE.— Gray  Copper  Ore. 

COMPOSITION. — Cu8Sb2S7.     Cu  often  partially  replaced  by  Fe, 
Zn,  Pb,  Hg,  Ag,  and  the  Sb  by  As. 


FIG.  392. 


FIG.  393. 


FIG.  394. 


GENERAL  DESCRIPTION. — A  fine  grained,  dark  gray  mineral  of 
metallic  lustre.  Characterized  especially  by  the  tetrahedral  habit 
of  its  crystals  which  are  sometimes  coated  with  yellow  chalcopyrite. 


FIG.  395. 


FIG.  396. 


CRYSTALLIZATION. — Isometric.  Hextetrahedral  class,  p.  62. 
The  tetrahedron  p,  Fig.  392,  usually  predominates,  often  modified 
by  the  tristetrahedron  n  =  (a  :  2a  :2a);  {211};  Figs.  395,  396, 
and  less  frequently  by  other  forms  such  as  the  dodecahedron  dt 
Fig.  393,  and  the  deltohedron  r  =  (a  :  a  :  2a);  {221} ;  Fig.  394. 


368  MINERALOGY. 

Physical  Characters.     H.,  3  to  4.5.     Sp.  gr.,  4.5  to  5.1. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  black  or  reddish  brown.  TENACITY,  brittle. 

COLOR,  light  steel  to  dark  lead  gray  or  iron  black. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  easily  to  a  globule 
which  may  be  slightly  magnetic.  Evolves  heavy  white  fumes 
with  sometimes  garlic  odor.  The  roasted  residue  gives  bead  and 
flame  reactions  for  copper.  Soluble  in  nitric  acid  to  a  green  solu- 
tion with  white  residue. 

SIMILAR  SPECIES. — The  crystals  are  characteristic.  The  fine 
grained  fracture  in  conjunction  with  the  color  is  often  sufficient  to 
distinguish  it.  It  is  softer  than  arsenopyrite  and  the  metallic 
cobalt  ores,  and  does  not  generally  yield  a  strongly  magnetic 
residue  on  heating.  Bournonite  and  chalcocite  are  softer,  and 
finally  the  blowpipe  reactions  are  distinctive. 

VARIETIES. — Tennanite — approximating  CusAs2S7,  but  grading 
into  ordinary  tetrahedrite  and  undistinguishable  by  crystal  form 
or  general  appearance. 

Freibergite,  argentiferous,  and  schwatzite,  "mercurial,  are  im- 
portant ores  respectively  of  silver  and  mercury.  Other  varieties 
carry  bismuth,  zinc  or  lead. 

REMARKS. — Tetrahedrite  is  one  of  the  most  frequent  minerals  of  the  copper 
deposits,  especially  in  veins  in  the  schists  and  older  eruptives.  Widely  distributed 
in  the  copper  veins  of  the  Andes,  porphyries  of  Chili,  the  Peruvian  Cordilleras  and 
Algeria.  Occurrences  are  numerous  in  Saxony,  Harz,  Hungary,  France,  Cornwall 
and  elsewhere. 

In  this  country  abundant  in  the  mines  of  Silverton  and  Aspen,  Colorado,  and  at 
Park  City,  Utah.  Also  is  found  in  the  mines  of  Butte,  Montana;  and  Bingham, 
Utah. 

Tennantite  occurs  in  crystals  in  Cornwall  and  massive  in  Mt.  Lyell,  Tasmania; 
Morococha,  Peru;  Teniente,  Chile;  Gilpin  County,  Colorado;  Laramie  County, 
Wyoming  and  sparingly  in  the  enargite  veins  at  Butte. 

CUPRITE. -— Red  Oxide  of  Copper,  Ruby  Copper  Ore. 

COMPOSITION.  —  Cu2O  (Cu  88.8  per  cent).  Sometimes  inter- 
mixed with  limonite. 

GENERAL  DESCRIPTION. —  Fine  grained  masses,  dark  red,  brown- 
ish-red and  earthy  brick-red  in  color ;  or  deep  red  to  crimson, 
transparent,  isometric  crystals,  usually  octahedrons,  or  cubes. 
Also  capillary. 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.      369 
FIG.  397.  FIG.  398.  FIG.  399. 


Sp.  gr.,  5.85  106.15. 
TRANSPARENT  to  opaque. 
TENACITY,  brittle. 


CRYSTALLIZATION.  —  Isometric.     Class  of  gyroid,  p.  66.     The 
octahedron  /,  cube  a  and  dodecahedron  d  predominating.      Index 
of  refraction  for  red  light  2.849. 
Physical  Characters.     H.,  3.5  to  4. 

LUSTRE,  adamantine  or  dull. 

STREAK,  brownish  red. 

COLOR,  crimson,  scarlet,  vermilion,  or  brownish  red. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  blackens  and  fuses  easily 
to  a  malleable  red  button.  Flame  and  bead  tests  give  the  color  for 
copper.  Soluble  in  nitric  acid  to  a  green  solution.  Soluble  also 
in  strong  hydrochloric  acid  to  a  brown  solution  which  diluted  with 
water  yields  a  white  precipitate. 

SIMILAR  SPECIES. — It  is  softer  than  hematite  and  harder  than 
cinnabar  or  proustite,  and  differs  from  them  all  by  yielding  an 
emerald-green  flame  and  a  malleable  red  metal  on  heating. 

REMARKS. — Chiefly  secondary,  part  in  the  gossan  intermixed  with  limonite  and 
in  part  developed  lower  as  in  limestones  where  copper  solutions  have  formed  carbon- 
ates. It  has  formed  the  principal  or  a  very  important  portion  of  deposits  at  Cobar, 
New  South  Wales;  Coro  Coro,  Bolivia;  Chessy,  France;  IllapeL  Chili;  many  mines 
in  Peru;  and  Boleo,  Lower  California.  In  the  United  States  it  is  especially  abundant 
in  the  Bisbee  district,  Arizona;  and  an  important  ore  in  certain  mines  in  Colorado, 
New  Mexico,  Nevada,  Wyoming  and  California. 

TENORITE. — Melaconite,  Black  Oxide  of  Copper. 

COMPOSITION. — CuO,  (Cu  79.85  per  cent.). 

GENERAL  DESCRIPTION. — Dull  black  earthy  masses,  black  powder  and  shining 
black  scales. 

PHYSICAL  CHARACTERS. — Lustre,  metallic  in  scales,  dull  in  masses.  Color  and 
streak  black.  H.,  3.  Sp.  gr.,  5.82  to  6.25. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  otherwise  like  cuprite. 

REMARKS. — Occurs  in  fissures  in  the  lava  of  Vesuvius,  as  a  black  coat  on  chalcopy- 
rite  and  as  dull  black  masses  with  chrysocolla. 

REMARKS. — Occurs  as  a  sublimation  product  at  Vesuvius  and  as  an  occasional 
decomposition  product  in  oxidized  zone  as  at  Bisbee,  Arizona,  and  Bingham,  Utah. 
25 


370  MINERALOGY. 

Said  to  occur  in  relatively  large  quantity  at  the  Rambler  Mine,  Wyoming,  and  in 
Waldo  district,  Oregon,  and  to  be  intermixed  with  the  secondary  chalcocite  of 
Ducktown,  Tenn. 

BROCHANTITE.— CuSO4  3Cu(OH)2.  Velvety,  emerald-green  crusts  of  fine 
orthorhombic  needle  crystals,  botryoidal  masses  and  vein-like  with  fibrous  structure. 
Transparent  to  translucent.  Lustre,  vitreous.  Streak,  pale  green.  H.,  3.5  to  4. 
Sp.  gr.,  3-9- 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  turns  black,  colors  the  flame -emerald 
green  and  leaves  malleable  red  button.  Insoluble  in  water,  but  soluble  in  acids.  In 
closed  tube  yields  water. 

REMARKS. — A  minor  ore  occurring  occasionally  in  oxidized  zone  and  sometimes 
in  economic  quantity,  as  at  Chiquicamata,  Chili;  Monarch  Mine,  Chaffee  Co., 
Colorado,  and  the  Clifton-Morenci  districts,  Arizona,  Coro  Coro,  Bolivia. 

ATACAMITE. 

COMPOSITION.— Cu(OH)Cl.Cu(OH)2>  (Cu  59-45,  Cl  16.64  per  cent.). 

GENERAL  DESCRIPTION. — Confused  aggregates  of  crystals  of  bright  or  dark-green 
color.  Also  granular  or  compact  massive,  or  as  a  crust.  Rarely  in  slender  ortho- 
rhombic  prisms. 

PHYSICAL  CHARACTERS. — Translucent  to  transparent.  Lustre,  adamantine  to 
vitreous.  Color,  bright  green,  emerald  green,  blackish  green.  Streak,  apple  green. 
H.,  3  to  3-5-  Sp.  gr.,  3.75  to  3-77- 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  yields  white  fumes  and  a  coating  which  is 
brown  near  the  assay  and  white  at  some  distance  from  it,  fuses  to  a  copper-red,  malle- 
able button,  and  colors  the  flame  a  beautiful  and  persistent  blue  "without  the  aid  of 
hydrochloric  acid.  In  closed  tube  yields  water  and  a  gray  sublimate.  Soluble  in  acids 
to  a  green  solution. 

REMARKS. — Found  in  large  quantities  in  Chili  in  the  oxidation  zone  at  Atacama, 
partly  as  sand  but  also  in  veins,  especially  at  Las  Remolinos,  Chili,  and  at  Toco- 
pilla,  Bolivia,  also  very  plentiful  at  Wallaroo,  South  Australia.  Minor  localities  are 
Boleo,  Lower  California;  Cornwall,  England;  Vesuvius  and  Etna. 

CHALCANTHITE.— Blue  Vitriol. 

COMPOSITION.— CuSO4-5H2O,    (CuO  31.8,  SO3  32.1,  K2O  36.1  per  cent.). 

GENERAL  DESCRIPTION. — A  blue, glassy  mineral,  with  a  disagreeable  metallic  taste. 
It  occurs  usually  as  an  incrustation,  with  fibrous,  stalactitic  or  botryoidal  structure;  but 
sometimes  in  flat  triclinic  crystals. 

PHYSICAL  CHARACTERS.— Translucent.  Lustre,  vitreous.  Color,  deep  blue  to 
sky  blue.  Streak,  white.  H.,  2.5.  Sp.  gr.,  2.12  to  2.30.  Brittle.  Taste,  metallic 
nauseous. 

CRYSTALLIZATION. — Triclinic.       Axes  a  :b~:  ^  =  0.566  : 

I  :  0.551.      Axial   angles  0  =  82°  21';  /?  =  73°  11';  7  =  77°  IG*  4°°' 

37'r  Prominent  forms,  right  and  left  unit  prisms  m  and  My 
unit  pyramid  /,  and  the  pinacoids  a  and  b.  Angles  mM= 
56°  50'.  Optically — . 

BEFORE  BLOWPIPE,  ETC.  —  On  charcoal,  fuses,  coloring 
flame  green  and  leaving  metallic  copper.  In  closed  tube 
yields  water  and  sulphur  dioxide  and  leaves  a  white  powder. 
Easily  soluble  in  water  to  a  blue  solution. 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.      371 


REMARKS. — Chalcanthite  is  of  great  interest  as  the  intermediate  stage  in  the  so- 
called  secondary  enrichment.  Often  present  in  the  waters  of  copper  mines,  from 
which  large  quantities  are  recovered  as  at  Rio  Tinto,  Spain,  and  at  Wicklow,  Ireland. 
Occasionally  found  in  quantity  and  mined,  as  at  Bluestone  Mine,  Lyon  County, 
Nevada;  United  Verde  Mine,  Arizona;  Copaquire,  Taraposa  and  Chiquicamata, 
[  Chili. 

MALACHITE.— Green  Carbonate  of  Copper. 

COMPOSITION.— Cu2(OH)2CO3,  (CuO  71.9,  CO2  19.9,  H3O  8.2 
per  cent.) 

GENERAL  DESCRIPTION. — Bright-green  masses  and  crusts,  often 
with  a  delicate,  silky  fibrous  structure  or  banded  in  lighter  and 
darker  shades  of  green.  Sometimes  stalactitic.  Also  in  dull- 
green,  earthy  masses,  and  rarely  in  small,  slender,  monoclinic 
crystals.  Frequently  coating  other  copper  minerals  or  filling 
their  crevices  and  seams. 

Physical  Characters.     H.,  3.5  to  4.     Sp.  gr.,  3.9  to  4.03. 
LUSTRE,  silky,  adamantine  or  dull.    TRANSLUCENT  to  opaque. 
Streak,  pale  green.  TENACITY,  brittle. 

COLOR,  bright  emerald  to  grass  green  or  nearly  black. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  decrepitates,  blackens, 
fuses,  and  colors  the  flame  green,  leaving  a  globule  of  metallic 
copper.  In  closed  tube,  blackens  and  yields  water  and  carbon 
dioxide.  Soluble  in  acids,  with  effervescence. 

SIMILAR  SPECIES. — Distinguished  by  color  and  effervescence 
with  acids. 

REMARKS. — Malachite  is  the  most  common  oxidation  product,  and  may  occur  in 
more  important  masses  in  the  zone  of  enrichment  by  replacement  of  limestone  or 
dolomite  or  as  a  later  alteration  of  other  secondary  minerals  such  as  chalcocite. 

The  purest  and  probably  largest  deposit  is  in  limestone  at  Mednorudiansk  near 
Nishni  Tagilsk,  which  yields  most  of  the  malachite  worked  into  art  objects.  Other 
famous  localities  are  Bisbee  and  Morenci,  Arizona;  Santa  Rita,  New  Mexico;  Cobar, 
New  South  Wales;  Bura  Burra,  Australia;  many  mines  in  Chili,  and  in  the  deposits 
in  sandstone  as  at  Coro  Coro,  Bolivia,  and  Perm,  Russia.  Often  it  occurs  pseudo- 
morphic  after  azurite  and  cuprite  as  at  Chessy,  France. 

AZURITE. — Blue  Carbonate  of  Copper. 

COMPOSITION.— Cu3(OH)2(CO3)2,  (CuO  69.2,  CO2  25.6,  H2O  5.2 
per  cent.). 

GENERAL  DESCRIPTION. — A  dark-blue  mineral  occurring  in 
highly  modified,  glassy,  monoclinic  crystals  and  groups.  When 


372 


MINERALOGY. 


massive,  it  may  be  vitreous,  velvety,  or  dull  and  earthy.  It  fre- 
quently occurs  incrusting  other  copper  ores,  or  distributed  through 
their  cracks  and  crevices. 

CRYSTALLIZATION. — Monoclinic.  Axes  &  :  b  :  c  =  0.850  :  i  : 
0.881 ;  ft  =  87°  36'. 

Crystals  very  varied  in  habit.     Those  figured  show  basal  pina- 

FIG.  401.  FIG.  402. 


Arizona.  Chessy,  France. 

coid  c,  ortho-pinacoid  a,  unit  prism  m,  unit  dome  <?,  and  the  pyra- 
mids /,  r,  and  v.  Supplement  angles  are  mm  =  80°  41 ';  co  =  44° 
46'.  Optically  +. 

Physical  Characters.     H.,  3.5  to  4.     Sp.  gr.,  3.77  to  3.83. 
LUSTRE,  vitreous.  TRANSLUCENT  to  opaque. 

STREAK,  blue.  TENACITY,  brittle. 

COLOR,  dark  blue  to  azure  blue. 

BEFORE  BLOWPIPE,  ETC. — As  for  malachite. 

REMARKS. — The  occurrences  of  azurite  are  essentially  those  of  malachite.  At 
Morenci,  Arizona,  and  Laurium,  Greece;  the  two  species  occur  in  concentric  bands. 
Splendid  crystals  were  found  at  Chessy,  France,  and  Bisbee,  Arizona. 

CHRYSOCOLLA, 

COMPOSITION. — CuSiO3  -f  2H2O.  Often  very  impure  (CuO  45.2, 
SiO2  34.3,  H2O  20.5  per  cent,). 

GENERAL  DESCRIPTION. — Green  to  blue  incrustations  and  seams 
often  opal-like  in  texture,  or  sometimes,  from  impurities,  resem- 
bling a  kaolin  colored  by  copper.  Also  brown,  resembling  limonite, 
and  in  dull  green  earthy  masses.  Never  found  in  crystals. 

Physical  Characters.     H.,  2  to  4.     Sp.  gr.,  2  to  2.3. 

LUSTRE,  vitreous,  dull.  TRANSLUCENT  to  opaque. 

STREAK,  white  to  pale  blue.  TENACITY,  brittle. 

COLOR,  green  to  light  blue,  brown  when  ferriferous. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     373 

BEFORE  BLOWPIPE,  ETC.  —  In  forceps  or  on  charcoal  is  infusible, 
but  turns  black,  then  brown  and  colors  the  flame  emerald  green.  In 
bead,  reacts  for  copper.  With  soda,  yields  malleable  copper.  In 
closed  tube,  yields  water.  Decomposed  by  hydrochloric  acid, 
leaving  a  residue  of  silica.  Boiled  with  KOH,  yields  a  blue  solu- 
tion, from  which  excess  of  NH4C1  precipitates  flocculent  H2SiOs. 

SIMILAR  SPECIES.  —  It  is  softer  than  turquois  or  opal  and  does  not 
effervesce  like  malachite. 

REMARKS.  —  Chrysocolla,  while  probably  present  in  lavas  and  basalts,  occurs 
principally  in  the  oxidation  zone.  It  is  an  important  ore  in  Gila  and  Final  Counties, 
Arizona;  Hartville,  Wyoming;  Bullion  District,  Nevada;  and  occurs  in  most  of  the 
prominent  copper-bearing  regions. 

THE  MERCURY  OR  QUICKSILVER  MINERALS. 

The  minerals  described  are: 

Metal  . 

Sulphides 


Selenides  and  Tellurides 


Chlorides 


Other  species  containing  mercury  are  amalgam  and  mercurial 

tetrahedrite.* 

ECONOMIC   IMPORTANCE. 

The  principal  ore  is  cinnabar,  though  mercury  is  obtained  from 
mercurial  tetrahedrite,  livingstonite,  terlinguaite  and  metallic 
mercury. 

The  world's  production!  is  between  4,000  and  5,000  short  tons 
per  year,  of  which  in  recent  years  Spain  has  furnished  about  one 
third  and  Italy,  Austria  and  the  United  States  each  from  one  fifth 
to  one  sixth  and  a  little  has  come  from  Mexico  and  other  countries. 

In  1915  this  country  produced^  775  tons,  of  which  522  came 
from  California,  the  rest  from  Nevada  and  Texas. 

In  these  deposits  and  in  most  others  there  is  close  association 
with  the  younger  volcanic  rocks.  Almaden  and  Nikitovka  belong 

*  Mineral  Resources  U.  S.,  1914,  p.  330. 

t  Engineering  and  Mining  Journal,  1916,  p.  67. 


Mercury 

Hg 

Cinnabar 

HgS 

Hexagonal 

Metacinnabarite 

HgS 

Isometric 

Livingstonite 

HgS.4Sb2S3 

Onofrite 

HgS.HgSe 

Tiemannite 

HgSe 

Isometric 

Coloradoile 

HgTe 

Calomel 

Hg2Cl2 

Tetragonal 

Terlinguaite 

Hg2C10 

Monoclinic 

374  MINERALOGY. 

to  an  earlier  period,  but  there  are  no  essential  genetic  differences.* 
In  general,  they  have  formed  near  the  surface  and  cease  with  a 
few  hundred  feet  of  depth.  The  most  constant  associate  is  pyrite, 
sometimes  marcasite;  the  other  common  sulphides  are  notably 
rare.  The  sulphides  of  antimony  and  arsenic  are  frequent  and 
asphalt-like  material  occurs  in  several  deposits. 

Mercury  is  obtained  from  cinnabar  by  heating  the  larger  lumps 
in  a  shaft-furnace,  resembling  a  continuous  lime  kiln,  with  three 
exterior  fire  places.  A  little  fuel  is  also  mixed  with  the  ore.  The 
heat  decomposes  the  sulphide,  forming  fumes  of  sulphur  dioxide 
and  mercury.  These  fumes  are  carried  off  through  large  iron 
pipes  to  condensers  where  the  mercury  is  liquified.  The  finer  ore  is 
heated  in  a  vertical  shaft  containing  a  series  of  inclined  shelves 
down  which  the  ore  slips  whenever  any  is  drawn  off  at  the  bottom. 
The  fumes  go  to  the  condensers  already  mentioned. 

The  principal  uses  of  mercury  are  in  making  fulminates  for 
explosive  caps  and  it  has  a  diminishing  use  in  certain  processes 
for  the  extraction  of  gold  and  silver  from  their  ores  and  in  the 
manufacture  of  vermilion.  Minor  uses  are  in  barometers,  ther- 
mometers and  electrical  appliances,  antiseptics  and  in  medicine. 

FORMATION   AND    OCCURRENCE    OF   MERCURY    DEPOSITS. 

Mercury  deposits  are  chiefly  found  filling  the  pores  and  cracks 
in  quartzite,  conglomerate  or  shattered  limestone.  At  Sulphur 
Bank,  Cat.,  and  at  Steamboat  Springs,  Nev.,  the  formation  is 
still  proceeding  and  it  is  believed  that  the  cinnabar  is  being  pre- 
cipitated from  solution  in  hot  waters  containing  excess  of  sodium 
sulphide  before  the  emergence  of  the  waters  and  as  a  result  of 
the  decomposition  of  the  sodium  sulphide.  Similar  depositions 
from  hot  sulphur  springs  have  been  observed  in  New  Zealand  and 
elsewhere. 

Almaden,  Spain. — The  deposits,  which  are  the  richest  and 
greatest  yet  discovered, §  consist  of  three  porous  beds — quartzites, 

separated  by  barren  clay  slates  (dipping  vertically  and  formerly 

— ' — —      ' 

*  Beyschlag,  Vogt  &  Krusch  (Truscott),  pp.  182,  461. 
t  Ibid.,  458. 

t  Beyschlag,  Vogt  &  Krusch  (Truscott),  182,  461 

§  Said  to  average  8  per  cent,  and  to  have  yielded  ore  equivalent  to  200,000  tons 
of  mercury. 


MINERALS   OF  METALLIFEROUS   ORE   DEPOSITS.     375 

regarded  as  veins),  the  cinnabar  partly  filling  the  pores  of  the 
quartzite  but  also  metasomatically  replacing  the  quartz  grains. 

Idria,  Austria. — The  cinnabar  is  in  shales  and  marls  and  fissures 
in  dolomite  and  there  are  many  fault  fissures.  Metallic  mercury 
occurs  in  the  underlying  clay  slates. 

California. — Along  the  coast  ranges  in  a  region  of  basalt  andesite 
and  rhyolite  as  fissure  veins  in  sandstone  widening  into  chambers,* 
and  as  tabular  masses  between  serpentine  and  sandstone. 

Mt.  Amiata,  Tuscany. — Near  trachyte  in  shales,  limestones, 
sandstones  and  the  trachyte  itself,  f 

Peru.— Many  deposits  exist  at  Huancavelica  and  Yauli,  Peru, 
in  a  region  of  slates,  conglomerates  and  limestone  near  trachyte 
inclusions.  They  are  now  unimportant,  formerly  enormous  pro- 
ducers. 

Avala,  Servia. — In  porous  quartz  rock  formed  by  alteration  of  a 
serpentine.  Cinnabar,  considerable  mercury  and  some  calomel. 

Nikitovka,  Russia. — In  clay  slate  beneath  sandstone  and  in 
fissures  in  coal  seams. 

Siberia. — With  gold  in  the  gravels  near  Beresowsk,  Miask,  etc. 

Terlingua,  Texas. — In  vertical  veins  in  limestone  and  in  breccia. 
Notable  for  the  chlorides  and  oxychlorides  found  there. 

Huitzuco,  Mexico. — As  cinnabar  and  stibnite  and  in  deeper 
levels  much  livingstonite. 

The  Mercurial  Tetrahedrite  Deposits. 

These  may  contain  as  much  as  17  per  cent.  Hg,  as  at  Dobschau 
and  Iglo,  Hungary,  in  veins  in  slate  where  the  mercury  is  recovered 
by  roasting  and  at  several  mines  near  Sumpter,  Oregon.  It  occurs 
also  at  Schwa tz,  Tyrol;  Landsberg,  Palatinate;  Mascara,  Bosnia; 

and  Ziks  Mts.,  Hungary. 

MERCURY. 

COMPOSITION. — Hg,  with  sometimes  a  little  silver. 

GENERAL  DESCRIPTION. — A  tin  white  liquid  with  metallic  lustre.  Usually  found 
in  little  globules  scattered  in  the  gangue,  or  in  cavities  with  cinnabar  or  calomel. 

PHYSICAL  CHARACTERS. — Opaque  liquid.  Lustre,  metallic.  Color,  tin  white. 
Sp.  gr.,  13.59. 

BEFORE  BLOWPIPE,  ETC. — Entirely  volatile.  In  matrass  or  closed  tube  may  be 
collected  in  small  globules.  Soluble  in  nitric  acid. 

*  Lindgren,  "Mineral  Deposits,"  p.  467. 

f  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  473. 


376  MINERAL  OGY. 

REMARKS. — Native  mercury  is  secondary  and  is  found  in  many  cinnabar  deposits 
and  sometimes  in  considerable  quantity,  as  at  the  Pioneer  and  other  mines  in  Cali- 
fornia; Terlingua,  Texas;  Idria,  Austria;  Avala,  Servia.  It  may  also  occur  without 
direct  contact  with  the  primary  deposit  as  in  marl,  near  Liineburg,  Hanover,  and  in 
cinnabar-free  strata  at  Almaden,  Spain. 

CINNABAR.— Natural  Vermilion. 

COMPOSITION. — HgS,    (Hg  86.2  per  cent.). 

GENERAL  DESCRIPTION. — Very  heavy,  bright  vermilion  to  brown- 
ish red  masses  of  granular  texture ;  more  rarely  small  transparent 
rhombohedral  crystals,  or  bright  scarlet  powder,  or  earthy  red  mass. 
Sometimes  nearly  black  from  organic  matter. 

Physical  Characters.     H.,  2  to  2.5.     Sp.  gr.,  8  to  8.2. 
LUSTRE,  adamantine  to  dull.  OPAQUE  to  transparent. 

STREAK,  scarlet.  TENACITY,  brittle  to  sectile. 

COLOR,  cochineal  red,  scarlet,  reddish  brown,  blackish. 

BEFORE  BLOWPIPE,  ETC.  —  Completely  volatilized  without  fusion 
if  pure.  With  soda  gives  sulphur  reaction.  In  closed  tube  yields 
a  black  sublimate,  which  becomes  red  when  rubbed  ;  if  soda  is  used 
a  metallic  mirror  is  obtained  instead  of  the  black  sublimate,  and  by 
rubbing  with  a  splinter  of  wood  globules  of  mercuiy  may  be  col- 
lected. If  cinnabar  powder  is  moistened  with  hydrochloric  acid  and 
rubbed  on  bright  copper  the  copper  is  made  silver  white.  Soluble 
in  aqua  regia. 

SIMILAR  SPECIES.  —  Cinnabar  is  softer  and  heavier  than  hematite, 
cuprite,  and  rutile.  It  has  a  more  decided  red  streak  than  crocoite 
or  realgar,  and  differs  from  proustite  in  density  and  blowpipe 
reactions. 

VARIETIES. — Hepatic  cinnabar  is  a  liver  colored  and  massive  or 
slaty  mixture  with  bitumen. 

Tile  ore  is  bright  red,  impure,  often  with  dolomite. 

REMARKS. — Occurring  as  stated,  p.  374.  Usually  primary,  sometimes  secondary f 
as  in  the  mines  near  Sumpter,  Oregon,  where  it  results  as  an  alteration  of  mercurial 
tetrahedrite.  In  this  country  it  occurs  in  San  Luis  Obispo,  Lake,  San  Benito,  Napa, 
Santa  Clara  and  other  counties,  California;  Terlingua,  Texas;  Bald-Butte,  Ore- 
gon. Humboldt  and  Nye  counties,  Nevada;  Idaho,  Utah  and  Washington  also  in- 
clude deposits. 

METACINNABARITE. — HgS  (Hg  86.2  per  cent.).  A  variety,  guadalcazarite, 
contains  a  little  selenium  and  zinc.  Amorphous  black  masses  and  hemispherical 
crystalline  aggregates  and  little  isometric  crystals  with  rough  faces.  Streak  black. 
H.,  3.  Sp.  gr.,  7.81.  Tests  as  for  cinnabar.  It  is  probably  secondary.  Occurs 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     377 

with  cinnabar  and  is  found  in  quantity  in  some  of  the  Californian  mines,  especially 
massive  at  New  Idria  and  in  crystals  at  the  Reddington  Mine.  Also  found  in  mercury 
deposits  of  Idria,  Austria;  Guadalcazar,  Mexico;  Bay  of  Islands,  New  Zealand;  and 
near  Otero,  Asturias,  Spain. 

LIVINGSTONITE.— HgSb4S7  (Hg  24.8,  Sb  53.1,  S  22.1  per  cent.).  Bright  lead- 
gray  prisms  and  columnar  masses  with  metallic  luster,  resembling  stibnite.  Streak 
red.  H.,  2.  Sp.  gr.,  4.1  to  4.8.  It  is  very  easily  fusible,  giving  heavy  white  fumes. 
Even  in  open  tube  gives  metallic  mercury.  Soluble  in  warm  nitric  acid  with  separa- 
tion of  antimony  trioxide. 

Found  thus  far  only  in  Mexico,  the  principal  deposit  being  at  La  Cruz  Mine, 
Huitzuco,  Mexico,  where  it  constitutes  practically  the  entire  ore  below  the  oxidized, 
zone  and  has  been  worked  to  a  depth  of  500  feet.  It  is  a  "stock  work"  in  limestone 
and  the  workings  follow  down  an  old  geyser  pipe. 

Small  amounts  are  found  also  at  Guadalcazar,  Mexico. 

ONOFRITE. — Hg(S,  Se).  In  metallic  blackish  gray  masses  resembling  chalco- 
cite.  Streak  blackish  gray.  H.,  2.5.  Sp.  gr.,  7.6  to  8.1. 

On  coal  decrepitates;  gives  copious  fumes  with  selenium  odor  and  lustrous 
sublimate,  which  will  color  the  R.  F.  blue.  In  closed  tube  with  soda  gives  mercury 
globules,  without  soda  gives  grayish  black  sublimate.  Insoluble  in  hydrochloric 
acid,  decomposed  by  aqua  regia  or  chlorine  gas. 

It  is  apparently  primary  and  occurs  at  Marysvale,  Utah,  with  tiemannite  as  a 
four-inch  vein  in  calcite  and  at  San  Onofre,  Mexico,  with  calcite  and  barite. 

TIEMANNITE.— HgSe  (Hg  71.7,  Se  28.3  per  cent.).  It  is  found  in  black  or 
nearly  black  fine-grained  masses  with  metallic  lustre  and  black  streak.  Rarely 
highly  modified  tetrahedral  crystals.  H.,  2.5.  Sp.  gr.,  7.1  to  8.5.  Tests  like 
onofrite. 

It  is  probable  primary  and  occurs  in  quantity  in  a  vein  in  limestone,  the  ore  some- 
times 4  feet  thick,  near  Marysvale,  Utah.  Found  also  at  Zorge  and  Tilkerode,  Harz, 
and  in  Argentina. 

COLORADOITE— COMPOSITION.— HgTe  (Hg  61.5,  Te  38.5  per  cent.).  It  is 
found  as  dense  masses  of  iron  black  material  sometimes  mottled  with  blue  or  purple 
H.,  3.  Sp.  gr.,  8.6. 

On  coal  volatilizes,  tinging  R.  F.  green  and  giving  white  sublimate.  In  closed 
tube  melts  and  gives  three  products,  globules  of  mercury,  drops  of  tellurium  dioxide, 
and  metallic  tellurium  nearest  the  assay.  Soluble  in  boiling  nitric  acid  with  separa- 
tion of  tellurium  oxide. 

It  is  found  in  small  amount  with  gold  and  silver  tellurides  in  Boulder  Co.,  Colorado 
and  as  a  mixture  with  gold  telluride  at  Kalgoorlie,  West  Australia. 

CALOMEL. — Horn  Mercury. 

COMPOSITION. — Hg2Cl2,  (Hg  84.9  per  cent.). 

•  GENERAL  DESCRIPTION. — A  gray  or  brown  translucent  mineral  of  the  consistency 
of  horn.  Usually  found  as  a  coating  in  cavities  with  or  near  cinnabar.  Sometimes 
in  well-developed  tetragonal  forms  c  —  1.723. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  adamantine.  Color,  gray,  white, 
brown.'  Streak,  white.  H.,  i  to  2.  Sp.  gr.,  6.48.  Very  sectile. 

BEFORE  BLOWPIPE,  ETC. — Volatilizes  without  fusion,  yielding  a  white  coating.  In 
closed  tube  with  soda  forms  a  metallic  mirror. 


378 


MINERALOGY. 


REMARKS. — Calomel  is  nowhere  an  important  source  6f  mercury,  but  is  a  secondary 
mineral  first  observed  in  the  old  deposits  in  the  Palatinate  and  since  that  in  many 
deposits,  notably  Avala,  Servia;  El  Doktor  near  Zimapan,  Mexico,  and  Terlingua, 
Texas. 

TERLINGUAITE.— Hg2ClO  (Hg  88.65,  Cl  7.85,  O  3.50  per  cent.).  Found  as 
small  transparent  sulphur  yellow  monoclinic  crystals  (the  name  is  also  used  for  yellow 
pulverulent  masses  from  same  locality).  It  becomes  olive  green  on  exposure.  H., 
2  to  3-  Sp.  gr.,  8.72. 

On  charcoal  volatilizes  completely,  giving  slightly  pinkish  sublimate.  On  closed 
tube  with  soda  gives  mercury  sublimate.  Soluble  in  nitric  acid. 

It  occurs  at  the  mercury  mines  of  Terlingua,  Texas,  in  a  vugg  in  a  calcite  vein. 

THE   SILVER   MINERALS. 

The  minerals  described  are: 


Metal 

Silver 

Ag 

Isometric 

Amalgam 

Ag2Hg3  to  AgseHg 

Isometric 

Sulphides 

Argentite 

Ag2S 

Isometric 

Stromeyerite 

CuAgS 

Orthorhombic 

Telluride 

Hessite 

Ag2Te 

Isometric 

Sulphoar  senile 

Proustite 

AgsAsSs 

Hexagonal 

Sulphoantimonites 

Pyrargyrite 

AgsSbSa 

Hexagonal 

Stephanite 

Ag5SbS4 

Orthorhombic 

Polybasite 

(Ag.Cu)9SbS6 

Orthorhombic 

Halides 

Cerargyrite 

AgCl 

Isometric 

."<•  '' 

Bromyrite 

AgBr 

Isometric 

£,mbolite 

Ag(Br.Cl) 

Isometric 

lodyrile 

Agl 

Hexagonal 

Most  of  the  silver  of  the  world  is  obtained  from  argentiferous 
galenite  and  silver.  Other  common  sulphides,  such  as  sphalerite, 
pyrite,  chalcopyrite,  chalcocite,  tetrahedrite,  etc..  and  their  oxida- 
tion products,  especially  cerussite,  are  often  silver  bearing.  Some- 
times it  occurs  in  manganese  or  iron  ores. 

There  are  many  other  species  containing  silver  among  which 
are  dyscrasite,  which  near  Wolfach,  Baden,  is  the  chief  silver  ore 
and  rare  species  like  rittingcrite,  pyrostilpnite,  polyargyrite, 
miargyrite,  argyrodite,  canfieldite,  naumannite,  and  eucairite. 

Argentiferous  tetrahedrite  occurs  plentifully  at  Elko  County, 
Nevada  and  Clear  Creek,  Colorado,  and  at  Pulacayo,  Bolivia; 
it  is  said  to  contain  ten  per  cent,  of  silver. 

THE    CUPELLATION   TEST   FOR    SILVER. 

The  only  satisfactory  test  is  cupellation.     Proceed  as  follows: 

The  iron  cupel  moulds,  Fig.  403,  are  pressed  full  of  finest  washed 

bone  ash,  placed  upon  the  anvil,  the  steel  stamp,  Fig.  403,  placed 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.      379 


vertically  upon  the  bone  ash  and  struck  with  the  hammer  until 
the  convex  side  of  the  stamp  touches  the  inner  side  of  the  mold 
on  all  sides. 

The  mold  is  then  placed  on  the  cupel  stand,  Fig.  404,  the  cross 
cuts  on  the  mold  diagonal  to  the  arms  of  the  stand. 


FIG.  403. 


FIG.  404. 


ROASTING. — The  ore  is  first  roasted  on  charcoal  to  remove 
volatile  constituents  and  then  one  volume  of  the  ore  is  mixed  with 
one  volume  of  borax  glass  and  one  to  two  volumes  of  test  lead. 

FUSION. — With  the  square  borer  a  deep  cylindrical  hole  is  bored 
in  the  charcoal  and  made  crucible  shaped  with  a  knife.  The  above 
mixture  is  carefully  placed  in  this  and  heated  in  a  pure  not  too 
strong  R.  F.  till  the  borax  and  lead  are  fused  and  then  the  heat 
is  made  greater  and  the  position  of  the  coal  occasionally  changed 
until  the  assay  turns  over. 

SOFTENING. — The  R.  F.  is  continued  till  no  small  lead  globules 
are  seen;  it  is  then  changed  to  a  moderate  O.  F.,  which  is  directed 
on  the  lead  in  order  to  volatilize  As,  Sb,  S,  etc.,  and  to  oxidize 
other  metals  and  make  them  unite  with  the  borax. 

When  the  slag  spreads  out  and  the  lead  begins  to  oxidize 
rapidly  and  rotate  the  blast  is  stopped,  the  assay  cooled,  the  lead 
and  slag  separated  by  hammering. 

SCORIFICATION. — The  cupel,  previously  prepared,  is  now  heated 
and  the  lead  placed  in  the  middle  and  fused  in  a  strong  O.  F., 
more  test  lead  being  added  if  needed.  After  fusing  a  pure  O.  F. 


380  MINERAL  OGY. 

is  used  and  a  moderate  red  heat.  The  blue  point  is  not  allowed  to 
touch  the  lead  and  the  oxide  cools  on  the  cupel  around  the  lead. 
After  awhile  the  position  of  the  cupel  stand  is  changed  and  the 
lead  moves  to  a  new  spot,  and  this  is  continued  until  the  lead  is 
reduced  to  a  button  of,  say,  2  mm.  diameter,  when  it  is  allowed  to 
cool  on  the  litharge  and  then  picked  out. 

If  before  the  button  is  reduced  to  this  size  the  oxide  accumulates 
in  such  quantity  as  to  interfere  with  the  work  the  scorification 
had  better  be  done  on  two  or  more  successive  cupels. 

FINE  CUPELLATION. — The  second  mold  is  then  heated  and  the 
button  placed  near  the  (higher)  left-hand  edge,  so  that  when  it 
melts  it  will  roll  to  the  middle  and  free  itself  from  adhering 
impurities. 

The  flame  is  then  directed  on  the  -bone  ash  around  the  button, 
not  on  the  button  itself  and  this  continued  till  all  lead  is  removed 
and  there  remains  only  a  silver  white  spherical  button  practically 
unaffected  by  further  blowing. 

ECONOMIC  IMPORTANCE. 

Ordinary  silver  ores  contain  less  than  one  per  cent,  of  the 
silver  compounds  distributed  through  various  earthy  and  metallic 
minerals,  and  only  show  the  true  nature  of  the  silver-bearing  sub- 
stance in  occasional  rich  specimens.  Frequently  an  ore  will  con- 
tain less  than  twenty  ounces  of  silver  per  ton.  On  the  other  hand 
very  rich  ores  occur  and  the  wonderful  deposits  at  Cobalt,  Ont., 
are  so  rich  that  masses  of  pure  native  silver  of  several  hundred 
pounds  weight  are  sometimes  secured. 

In  1915  the  United  States  produced  67,485,600  ounces,  which  is 
somewhat  less  than  a  third  of  the  world's  production.* 

The  silver  production!  of  the  world  for  1914  is  given  as  215,700,- 
394  oz.,  of  which  this  country  produced  67,929,700  oz.,  or  31  per 
cent.,  and  Canada,  27,544,231  oz.,  or  13  per  cent.  Mexico,  the 
other  great  producer,  in  1913  produced  49,461,103  oz.  Australia, 
Germany,  Belgium  and  Japan  also  produce  in  the  millions  of 
ounces. 

The  states  producingt  over  one  million  ounces  in  1914  were: 

*  Engineering  and  Mining  Journal,  1916,  p.  43. 

f  Mineral  Industry,  1914,  p.  282. 

J  Mineral  Resources  U.  S.,  1914,  p.  829  and  857. 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.     381 

Ounces.  Ounces. 

Nevada 15,877,200  Colorado 8,804,400 

Idaho 12,573,800  Arizona 4,439,500 

Montana 12,536,700  California 2,020,800 

Utah 11,722,000  New  Mexico 1,771,300 

The  sources  of  the  silver  were: 

Ounces. 

Dry  and  siliceous  ores 28,000,875 

Argentiferous  lead  ores 19,302,081 

Copper  ores  (over  2^  per  cent.  Cu) 14,829,828 

Zinc  ores  (over  25  per  cent.  Zn) 145,264 

Lead  zinc  ores 7,132,747 

Copper  lead  zinc  ores 248,806 

Refining  placer  gold 152,128 

SMELTING. — The  extraction  of  silver  by  reduction  with  lead- 
ores  in  a  water-jacket  furnace,  and  the  subsequent  treatment  has 
been  referred  to  under  lead,  p.  317.  When  silver  is  a  constituent 
of  a  copper  matte  it  is  recovered  as  a  sedimentary  product  in  the 
electrolytic  refining  of  the  copper.  It  is  collected,  together  with 
any  gold  present,  and  further  purified. 

AMALGAMATION. — Native  silver  and  the  chloride,  bromide  and 
iodide  can  be  extracted  by  the  use  of  mercury  while  argentite  and 
some  other  ores  can  be  amalgamated  by  the  addition  of  chemicals 
(copper  sulphate,  salt,  etc.)  and  in  other  cases  there  may  be  a 
pre -roasting  with  salt  to  form  chlorides. 

The  principle  is  that  mercury  will  reduce  certain  compounds 
of  silver  to  metal  and  unite  with  the  silver,  or  if  mercury  is  present 
and  some  other  substance,  as  iron  or  copper,  reduces  the  ore  to 
silver,  the  mercury  will  collect  it. 

In  pan  amalgamation,  less  used  than  formerly,  the  finely-crushed  ore,  mixed  to  a 
pulp  with  water,  is  charged  into  a  tub-like  vessel,  with  an  iron  bottom  and  wooden 
sides.  In  this  tub  or  pan  there  revolves  a  stirrer,  with  arms  shaped  to  throw  the 
pulp  to  the  sides,  from  which  it  rolls  back  to  the  center.  Attached  to  the  arms  are 
grinding  shoes,  which  can  be  lowered  so  as  to  rub  on  the  iron  bottom  or  be  raised 
free  from  it.  Generally  the  pulp  will  be  kept  hot  by  steam,  and  no  mercury  will  be 
added  until  the  grinding  is  completed.  During  the  grinding  the  metallic  iron  of  the 
bottom  and  the  shoes  reduces  the  silver  compound ;  although  chemicals,  such  as  salt, 
copper  sulphate,  potassium  cyanide,  etc.,  are  sometimes  added  to  assist. 

In  treating  the  rich  native  silver  of  Nipissing,  Ontario,  a  combina- 
tion of  amalgamation  and  cyaniding  is  used. 

The  ore  with  an  average  content  of  2,600  oz.  Ag  per  ton,  6  per  cent.  Ni,  7-8  per 
cent.  Co,  and  40  per  cent.  As,  is  crushed  to  70  mesh  and  ground  for  9  hours,  in  a  Krupp 
tube  mill  with  3  Y^  tons  ore,  4^  tons  of  mercury  and  a  five  per  cent,  cyanide  solution. 


382  MINER  ALOG  K 

It  is  then  settled  by  gravity,  the  amalgam  removed.  The  silver  in  the  cyanide 
pulp  is  then  precipitated  on  zinc  shavings. 

The  excess  mercury  in  either  case  is  strained  from  the  amalgam  and  the  residue 
distilled  off  in  retorts. 

The  refining  involves  melting.  At  Nipissing  a  reverberatory  furnace  is  used  and 
fifteen  hours  of  oxidation,  after  which  the  silver  is  cast. 

HYDROMETALLURGY. — Cyaniding  is  principally  used  in  this 
country,  dilute  solutions  of  potassium  cyanide  rarely  higher  than 
0.7  per  cent,  dissolving  most  silver  minerals,  but  native  silver  only 
slowly  and  copper-bearing  minerals  like  polybasite  being  objection- 
able. The  leaching  may  continue  10  to  25  days,  the  silver  then 
being  precipitated  on  zinc  dust  or  zinc  shavings. 

At  Tonopah,  Nevada,  a  mixed  ore  of  polybasite,  stephanite,  argentite,  some 
selenide  of  silver  and  secondary  cerargyrite,  iodyrite  and  native  silver  is  crushed  in 
gyratory  crushers,  then  stamped  in  weak,  warm  KCy  solutions  (60  to  90°  C.)  and 
reduced  to  slimes  in  tube  mills.  It  is  then  agitated  48  hours  with  addition  of  cyanide, 
lime  and  lead  acetate,  precipitated  with  zinc  dust,  filtered,  dried  and  melted  in 
graphite  crucibles. 

The  uses  of  silver  are  too  well  known  to  need  repeating. 

FORMATION  AND  OCCURRENCE  OF  SILVER  DEPOSITS. 
Analyses  show  the  presence  of  silver  in  minute  amounts  in  both 
igneous  and  sedimentary  rocks,  and  an  estimate  of  .00001  per  cent, 
is  made  for  the  crust  of  the  earth.  It  is  present  in  the  magmatic 
segregations  in  gabbro,  of  Sudbury,  Canada,  and  Scandinavia. 
The  economic  occurrences  may  be  classified  as  follows: 

The  "  Young  "  Veins. 

These  veins,  which  usually  cross  all  rocks  and  obviously  repre- 
sent the  latest  stage  of  eruption,  are  always  connected  with  the 
later  eruptive*  rocks,  often  occurring  in  volcanic  chimneys  or 
"necks"  and  the  adjacent  rock  and  frequently  by  abnormal 
increases  of  temperature  and  presence  of  gases  and  hot  springs 
showing  their  nearness  to  volcanic  activities. 

Mineralogically  they  differ  from  the  older  veins,  in  the  occur- 
rence together  of  notable  amounts  of  both  gold  and  silver  minerals, 
the  rich  silver  minerals  are  relatively  abundant,  especially  the 
sulpho  salts,  proustite,  pyrargyrite,  stephanite,  tetrahedrite,  and 
polybasite,  while  a  quartz  gangue  and  arsenic  and  antimony  min- 

*  Especially  andesite,  dacite,  often  rhyolite,  sometimes  trachyte,  phonolyte 
very  seldom  basalt.  Beyschlag,  Vogt  &  Krusch  (Truscott),  516. 


MINERALS    OF  METALLIFEROUS   ORE  DEPOSITS.     383 

erals  are  common.  The  common  sulphides  occur,  but  nickel  and 
cobalt  are  rare. 

The  great  development*  of  the  young  gold  silver  veins  follows 
the  mountain  chains  on  each  side  of  the  Pacific,  especially  the 
Great  Basin  of  the  United  States,  Mexico,  the  Andes  of  Chili, 
Bolivia,  etc.,  Japan,  Philippines,  Borneo  and  east  coast  of  Asia. 

Examples  are: 

Pachuca,  Mexico. — Rich  silver  minerals  in  veins  which  cut 
andesite  rocks  and  adjacent  sediments.  The  gangue  is  quartz, 
rhodonite,  rhodochrosite,  andularia.  The  silver  minerals  are 
argentite,  stephanite,  polybasite,  with  pyrite,  galenite  and  sphaler- 
ite. In  the  upper  portions  limonite  and  the  horn  silvers  (cerar- 
gyrite,  bromyrite,  etc.). 

Tonopah,  Nevada. — Rich  silver  minerals  and  gold.  Veins  in 
andesite  and  rhyolite.  The  gangue  is  quartz,  rhodonite,  adularia, 
etc.  The  silver  minerals  are  principally  argentite  and  polybasite 
with  fine  gold  and  in  the  oxidized  zone  much  cerargyrite  with 
iodyrite  and  bromyrite.  Below  this  secondary  argentite,  poly- 
basite and  pyrargyrite. 

Chanarcillo,  Chili. — Rich  silver  minerals  with  copper  minerals 
in  limestone  cut  by  augite  porphyry  and  these  rocks  by  the  veins. 
In  the  upper  levels  silver,  cerargyrite,  bromyrite,  malachite, 
siderite  and  barite  in  yellow  clay;  below  this  silver,  argentite, 
polybasite,  proustite,  pyrargyrite;  in  the  lower  levels,  sphalerite, 
galenite,  arsenopyrite  and  pyrite. 

Pulacayo,  Bolivia. — Copper  and  lead  minerals  rich  in  silver  but 
not  the  rich  silver  minerals  to  any  extent.  Veins  in  andesite  and 
trachyte;  the  gangue,  barite  and  quartz;  the  ore  sphalerite,  chal- 
copyrite,  galenite  and  tetrahedrite  all  silver-bearing. 

Las  Chispas,  Sonora. — Rich  silver  minerals  in  quartz  veins  in 
rhyolite  and  tuff.  The  first  200  feet  cerargyrite  and  some  gold; 
the  lower  levels  stephanite  in  large  masses,  argentite,  pyrargyrite 
and  polybasite.  Also  argentiferous  hematite. 

The  "  Old  "  Veins. 

The  silver  and  gold  are  less  together  than  in  the  new  veins  and 
the  old  veins  show  in  generalf  less  connection  with  eruptive 
magmas  and  if  observed  the  eruptives  are  old. 

*Ibid.,  515. 

t  Beyschlag,  Vogt  &  Krusch  (Truscott),  601. 


384  MINERAL  OGY. 

Quartz  silver  lodes  are  rare  in  the  old  veins,  dominant  in  the  new. 
Mineralogically,  probably  because  of  longer  erosion,  since  rich 
silver  minerals  occur  near  the  surface,  and  the  deposits  worked  are 
chiefly  the  deep  primary  ores  of  lead,  zinc,  copper.  The  gangue  may 
include  silicates,  as  at  Kongsberg,  axinite,  elsewhere  adularia,  etc. 

Examples  are: 

Kongsberg,  Norway* — Rich  silver  minerals  in  narrow  veins  in 
gneiss  and  mica  schist.  The  chief  ore  is  silver,  believed  to  be  an 
alteration  of  earlier  and  now  rare  argentite  and  proustite.  There 
is  some  stephanite.  An  unusual  feature  is  numerous  zeolites 
(stilbite,  laumontite,  harmotone,  etc.). 

Cobalt,  Ontario.^ — Metallic  silver  with  cobalt  minerals.  Vol- 
canic rocks,  greenstones  and  schists,  covered  by  conglomerate, 
are  cut  by  "  sills  "  of  diabase.  The  ore  is  in  veins  in  the  later  formed 
crevices,  cutting  all  rocks  and  richest  in  the  conglomerates.  The 
principal  silver  mineral  is  native  silver,  but  argentite,  dyscrasite, 
and  pyrargyrite  also  occur.  These  are  with  older  formed  smaltite, 
niccolite  and  other  cobalt  nickel  and  bismuth  minerals. 

Others  are  Freiberg,  Saxony;  Andreasberg,  Harz;  Pfibram, 
Bohemia;  Butte,  Montana. 

Metasomatic  Replacements. 

Aspen,  Colorado. — Rich  silver  minerals  with  galenite  and  spha- 
lerite replacing  limestone.  Limestone,  dolomite  and  shales  are  cut 
by  diorite  and  rhyolite  porphyry.  The  mineral  solutions  ascending 
in  the  faults  and  fissures  with  gradually  rising  temperature  de- 
posited first  veins  of  barite  with  some  native  silver,  then  rich  silver 
ores  argentite  and  polybasite,  and  finally  the  galenite  and  sphaler- 
ite as  replacements  of  the  limestone. 

Leadville,  Colorado. — Lead,  zinc  and  manganese  minerals  with 
silver.  Shales,  limestones  and  quartzite  are  cut  by  granite 
porphyry  intrusions.  The  ores  are  near  the  contact  as  replace- 
ments in  the  limestone,  the  primary  ore  being  a  granular'  mixture 
of  sulphides.  The  upper  levels  are  chiefly  earthy  mixtures  of 
cerussite  and  cerargyrite  in  clayey  limonite.  Other  metasomatic 
deposits^  exist  at  Eureka,  Nevada;  Park  City  and  Tintic  Utah 

*  ibid.,  660. 
t  Ibid.,  666. 
JLindgren,  "Mineral  Deposits,"  p.  569. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.     385 

Lake  Valley,  New  Mexico;  and  with  many  copper  and  lead  ores 
carrying  silver. 

Contacts. 

Broken  Hill,  New  South  Wales* — Lead  and  zinc  minerals  with 
silver  minerals.  A  complex  of  gneiss,  schists  and  quartz  garnet 
rock  is  cut  by  diorite  dikes.  The  contact  deposit  primary  ores 
are  sphalerite  and  galenite  with  garnet  all  through  the  ore.  Near 
the  surface  there  is  chiefly  manganiferous  limonite,  then  a  zone 
of  silver-bearing  cerussite  with  cerargyrite  and  silver  and  smaller 
quantities  of  embolite  and  iodyrite.  Below  this  are  the  unaltered 
primary  ores. 

The  veins  of  the  Horn  Silver  Mine,  Frisco,  Utah,  occurf  at  the 
contact  of  rhyolite  and  limestone. 

In  Sediments. 

Silver  Reef,  Utah. — Rich  silver  minerals  in  Triassic  sandstone 
due  to  secondary  concentrationf  from  argentiferous  chalcocite. 
Above  the  water  level  cerargyrite,  below  the  water  level  silver, 
argentite  and  argentiferous  chalcocite. 

SILVER.— Native  Silver. 

COMPOSITION. — Ag,  sometimes  alloyed  with  Au,  Cu,  Pt,  Hg, 
Sb,  Bi. 

GENERAL  DESCRIPTION. — A  silver-white,  malleable  metal  oc. 
curring  in  masses,  scales  and  tw'sted  wire-like  filaments,  pene- 
trating the  gangue  or  flattened  upon  its  surface.  .Sometimes 
in  isometric  crystals,  occasionally  sharp  but  more  frequently 
elongated  and  needle-like  or  in  aborescent  groups,  each  branch  of 
which  is  composed  of  distorted  forms  in  parallel  position. 

Physical  Characters.     H.,  2.5  to  3.     Sp.  gr.,  10.1  to  ii.i. 
LUSTRE,  metallic.  •       OPAQUE. 

STREAK,  silver  white.  TENACITY,  malleable. 

COLOR,  silver  white,  tarnishing  brown  to  nearly  black. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses  to  a  white  metallic 
globule.  Soluble  in  nitric  or  sulphuric  acid,  but  from  these  it  is 

*  Beyschlag,  Vogt  and  Krusch  (Truscott),  400. 

t  Ibid.,  558. 

t  Lindgren,  "Mineral  Deposits,"  p.  374. 

26 


386  MINER  ALOG  Y. 

precipitated  as  a  white  curd-like  precipitate  by  hydrochloric  acid 
salt.     The  precipitate  darkens  on  exposure  to  light. 

SIMILAR  SPECIES.  —  When  tarnished,  silver  resembles  copper  or 
bismuth,  but  is  distinguished  by  its  silver-white  streak  from  the 
former  and  by  malleability  and  non-volatilization  from  the  latter. 

REMARKS. — Silver  is  said  to  be  a  primary  mineral  at  Mogollon,  Socorro  Co.,  New 
Mexico,  but  is  usually  secondary  and  often  found  at  considerable  depth.*  It  is 
found  to  some  extent  in  nearly  all  deposits  containing  rich  silver  minerals  and  some- 
times with  lead  or  copper  minerals.  In  some  localities,  as  at  Cobalt,  Ontario,  it  is 
the  dominating  mineral. 

The  most  celebrated  mines  where  native  silver  is  obtained  are  those  of  Kongsberg, 
in  Norway,  and  Huantaya,  Peru.  Others  are  in  Sonora,  Mexico;  the  Michigan 
copper  region;  Boulder  Co.,  Colorado;  Butte,  Montana;  Poor  Mans  Lode,  Idaho; 
Silver  King,  Arizona. 

It  is  found  in  several  localities  with  zeolites,  as  in  Andreasberg,  Harz;  Arqueros, 
Chili;  Kongsberg,  Norway,  and  with  the  copper  of  Lake  Superior. 

AMALGAM. 

COMPOSITION. — Ag2Hgs  to  AgaeHg. 

GENERAL  DESCRIPTION. — A  brittle,  silver-white  mineral  of  bright  metallic  lustre, 
which  occurs  in  imbedded  grains  and  indistinct  isometric  crystals. 

PHYSICAL  CHARACTERS. — Opaque,  lustre  metallic.  Color  and  streak,  silver  white. 
H.,  3  to  2.5.  Sp.  gr.,  13.75  to  14.1.  Somewhat  brittle  and  cuts  with  a  peculiar 
grating  noise. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  partially  volatilized,  leaving  malleable 
silver.  In  closed  tube,  yields  mercury  mirror.  Soluble  in  nitric  acid. 

REMARKS. — Amalgam  is  frequently  found  in  mercury  mines  in  small  amounts, 
as  at  Ober  Moschel,  Bavaria;  Idria,  Austria,  and  near  Almaden,  Spain  It  is  occa- 
sionally found  in  silver  deposits,  as  at  Arqueros,  Chili,  and  the  silver  of  Kongsberg, 

Norway,  carries  mercury. 

• 

ARGENTITE.  —  Silver  Glance. 

COMPOSITION. — Ag2S,  (Ag  87.1  per  cent). 
GENERAL  DESCRIPTION. — A  soft  black  mineral,  of  metallic  lustre, 
which  cuts  like  wax  and  occurs  as  masses,  disseminated  grains,  or 
incrusting.  Also  found  as  isometric  crystals,  the  cube,  octahe- 
dron, or  dodecahedron  being  most  common  and  frequently  grouped 
in  parallel  positions. 
Physical  Characters.  —  H.,  2  to  2.5.  Sp.  gr.,  7.2  to  7.36. 

LUSTRE,  metallic.  OPAQUE. 

STREAK,  lead  gray.  TENACITY,  very  sectile. 

COLOR,  lead  gray  to  black  or  blackish  gray. 

BEFORE   BLOWPIPE,  ETC. — On   charcoal,   swells,   fuses,  yields 

*  At  Aspen,  Colorado,  900  feet  below  surface.     Ibid.,  586. 


MINERALS   OF  METALLIFEROUS    ORE   DEPOSITS.      387 

fumes  of  sulphur  dioxide,  and   finally   mallable  silver.     Soluble 
in  nitric  acid,  with  separation  of  sulphur. 

SIMILAR  SPECIES. — Differs  from  other  soft  black  minerals  in 
cutting  like  wax  and  in  yielding  malleable  silver  on  heating.  Dif- 
fers from  cerargyrite  in  solubility  in  nitric  acid. 

REMARKS. — Is  both  primary  and  a  product  of  secondary  enrichment.*  Large 
quantities  have  been  obtained  at  Tonopah  and  Comstock  and  Austin,  Nevada; 
Pachuca,  Mexico;  Chafiarcillo,  Chili;  and  Aspen,  Colorado,  and  fine  crystals  from 
Arizpe,  Sonora,  and  Freiberg,  Saxony. 

STROMEYERITE 

COMPOSITION. — CuAg  S,  (Ag  53.1;  Cu  31.1  per  cent.). 

GENERAL  DESCRIPTION- — Dark  gray  metallic  masses  resembling  chalcocite. 
Rarely  twinned  orthorhombic  crystals. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color,  dark  gray.  Streak, 
same  as  color.  H.,  2.5-3.  Sp.  gr.  6.2-6.3. 

BEFORE  BLOWPIPE,  ETC. — Reacts  for  copper,  silver  and  sulphur. 

REMARKS. — Stromeyerite  is  found  in  quantity  at  the  Yankee  Girl  Mine,  Ouray  Co,. 
Colorado,  and  in  smaller  amounts  at  other  localities  in  Colorado,  California,  Nevada 
and  Arizona.  Foreign  occurrences  exist  in  Siberia,  Silesia,  Peru,  Argentina  and 
Tasmania. 

HESSITE. 

COMPOSITION. — (Ag-Au)2Te,  grading  from  hessite,  Ag2Te  (Ag  63 
per  cent.)  to  petzite,  in  which  there  is  20  to  25  per  cent,  of  gold. 

GENERAL  DESCRIPTION. — Fine-grained,  gray,  massive  mineral, 
of  metallic  lustre.  Also  coarse  granular,  and  in  small,  indistinct, 
isometric  crystals. 

Physical  Characters.     H.,  2  to  2.5.     Sp.  Gr.,  8.3  to  8.6. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  black.  TENACITY,  slightly  sectile. 

COLOR,  between  steel  gray  and  lead  gray. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses  to  a  black  globule, 
with  white  silver  points  on  its  surface.  If  powdered  and  dropped 
into  boiling  concentrated  sulphuric  acid,  the  acid  is  colored  an 
intense  purple. 

REMARKS. — Hessite  has  been  an  important  ore  in  Boulder  Co.  and  La  Plata  Co., 
Colorado,  and  occurs  in  Calaveras  Co.,  California,  and  Baker  Co.,  Oregon.  The 
best  known  occurrences  are  in  Transylvania,  Hungary.  Also  found  in  Altai,  Siberia, 
and  Arqueros,  Chili. 

*  In  the  zone  of  enrichment  it  is  usually  accompanied  by  the  sulpho  salts  such  as 
proustite,  pyrargyrite  and  stephanite. 


388  MINERALOGY. 

THE   SULPHO-SALTS    OF   SILVER. 

The  sulpho-salts  of  silver,  proustite,  pyrargyrite,  stephanite, 
polybasite,  frequently  occur  together  and  with  argentite  and 
silver  form  the  enriched  zone  in  many  mines.  Their  mode  of 
formation  is  not  understood  and  one  of  them  at  least,  polybasite, 
is  believed  to  sometimes  be  primary. 

PROUSTITE.— Light  Ruby  Silver. 

COMPOSITION.— Ag3AsS3,  (Ag  654,  As  15.2,  S  19.4  per  cent.). 
Sometimes  containing  a  little  antimony. 

GENERAL  DESCRIPTION. — A  scarlet  vermilion  mineral,  either 
translucent  or  transparent,  with  a  scarlet  streak.  Usually  occurs 
disseminated  through  the  gangue  or  as  a  stain  or  crust.  Rarely 
in  small  hexagonal  crystals. 

CRYSTALLIZATION. —  Hexagonal.  Hemimorphic 
class,  p.  52.  Axis  ^  =  0.804.  Fig.  405  shows  a 
typical  crystal  according  to  Miers.  Optically—,  with 
very  high  indices  of  refraction  (j  =  2.979  for  red 
light). 

Physical  Characters.      H.,   2   to   2.5.     Sp.   gr.,   5.57 
to  5.64. 

LUSTRE,  adamantine,  brilliant.      TRANSLUCENT  to  transparent. 
STREAK,  scarlet.  TENACITY,  brittle. 

COLOR,  scarlet  vermilion. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses,  yields  sulphurous 
and  garlic  odors  and  malleable  silver.  In  closed  tube,  fuses  and 
yields  slight  red  sublimate,  yellow  when  cold.  Decomposed  by 
nitric  acid,  leaving  a  white  residue.  In  powder,  is  turned  black  by 
potassium  hydroxide  solution,  and  partially  dissolved  on  boiling. 
Hydrochloric  acid  precipitates  from  this  a  lemon  yellow  arsenic 
sulphide. 

SIMILAR  SPECIES. — Differs  from  pyrargyrite  in  scarlet  streak, 
and  from  cuprite  and  cinnabar  by  garlic  odor  when  heated. 

REMARKS. — Proustite  is  less  abundant  than  pyrargyrite  and  probably  than 
polybasite  and  may  accompany  them  below  the  oxidized  zone.  Famous  deposits 
were  worked  at  Chafiarcillo  and  Caracoles,  Chili,  and  Guanajuato,  Mexico,  and 
other  well-known  localities  are  St.  Andreasberg,  Harz,  and  the  silver  cobalt  deposits 
at  and  near  Freiberg,  Saxony,  and  Joachimsthal,  Bohemia.  Most  abundant  in  the 
United  States  at  Poor  Man's  Lode,  Idaho;  Austin,  Nevada,  and  in  Gunnison  County, 
Colorado,  at  the  Ruby  silver  district. 


MINERALS   OF  METALLIFEROUS    ORE  DEPOSITS.      389 

PYRARGYRITE.— Dark  Ruby  Silver. 

COMPOSITION. — Ag3SbS3,  (Ag  59.9,  Sb  22.3,  S  17.8  per  cent.), 
Often  with  small  amounts  of  arsenic. 

GENERAL  DESCRIPTION. — A  nearly  black  mineral,  which  is  deep 
red  by  transmitted  light  and  has  a  purplish-red .  streak.  Usually 
occurs  massive  or  disseminated,  or  in  thin  films,  sometimes  in 
crystals. 

FIG.  406.  CRYSTALLIZATION.  —  Hexagonal.     Hemimorphic 

class,  p.  52.  Axis  ^=0.789.  Prismatic  crystals, 
with  rhombohedral  or  scalenohedral  terminations. 
Frequently  twinned.  Fig.  406  shows  a  typical 
crystal  according  to  Miers.  Optically  — ,  with  very 
high  indices  of  refraction  (j  =  3.084  for  red  light). 

Physical  Characters.     H.,  2.5.     Sp.  gr.,  5.77  to  5.86. 

LUSTRE,  metallic,  adamantine.  TRANSLUCENT  to  opaque. 

STREAK,  purplish  red.  TENACITY,  brittle. 

COLOR,  black  or  nearly  so,  but  purple  red  by  transmitted  light. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal,  fuses  easily,  spirts, 
evolves  dense  white  fumes  and  leaves  malleable  silver,  A  white 
sublimate  forms.  In  closed  tube,  yields  black  sublimate,  red 
when  cold.  Soluble  in  nitric  acid,  with  separation  of  sulphur 
and  antimony  trioxide.  In  powder,  is  turned  black  by  a  solution 
of  potassium  hydroxide,  and  on  boiling  it  is  decomposed  ;  the  solu- 
tion deposits  an  orange  precipitate  on  addition  of  hydrochloric 
acid. 

SIMILAR  SPECIES.  —  The  streak  is  purplish  red,  differing  from  the 
scarlet  of  proustite.  The  streak  and  silver  reaction  distinguish  it 
from  cuprite,  cinnabar  and  realgar. 

REMARKS. — Pyrargyrite  is  more  abundant  than  proustite  and  is  found  in  im- 
portant quantities  in  many  localities  as  at  Guanajuato  and  Sonora,  Mexico;  Chafiar- 
cillo  and  Caracoles,  Chili;  Poor  Man's  Lode,  Idaho;  Austin  and  Reese  River, 
Nevada;  Stockton  Hill  District,  Arizona.  Other  well-known  localities  are  St. 
Andreasberg,  Harz;  Pfibram,  Bohemia;  Freiberg,  Saxony;  Schemnitz  and  Kremnitz, 
Hungary. 

STEPHANITE  —  Brittle  Silver  Ore. 

COMPOSITION.— Ag5SbS4,    (Ag  68.5,  Sb  15.2,  S  16.3  per  cent.). 

GENERAL  DESCRIPTION. — Fine-grained,  iron-black  mineral,  with 
metallic  lustre,  often  disseminated  through  the  gangue.  Some- 
times in  short  six-sided  prismatic  crystals.  It  is  soft,  but  brittle. 


390  MINERAL  OGY. 

CRYSTALLIZATION.  —  Orthorhombic.       Axes 
a  \~b:c  =  0.629  :    i  :  0.685.     Short    prismatic  ^  4°1- 

crystals  often  twinned  in  pseudo-hexagonal 
shapes.  Unit  pyramid  p,  unit  prism  m,  the 
pinacoids  b  and  c  and  the  dome  /=  (oo  d  : 
~b  :  2c)  ;  {021}  ;  are  the  commoner  forms.  Sup- 
plement angles  mm  =  64°  21'  ;  //  =  49°  44' ;  <r/~=  53°  53'. 

Physical  Characters.     H.,  2  to  2.5.     Sp.  gr.,  6.2  to  6.3. 

LUSTRE,  metallic.  OPAQUE. 

STREAK  and  COLOR,  black.  TENACITY,  brittle. 

BEFORE  BLOWPIPE,  ETC.— On  charcoal,  fuses  easily,  yielding 
white  fumes  and  coat  and  odor  of  sulphur  dioxide,  finally  leaves 
malleable  silver.  Soluble  in  nitric  acid,  with  residue  of  sulphur 
and  antimony  tri oxide.  With  potassium  hydroxide,  reacts  like 
pyrargyrite. 

SIMILAR  SPECIES. — It  is  more  brittle  than  argentite  and  softer 
than  tetrahedrite. 

REMARKS. — Stephanite  is  sometimes  secondary  after  polybasite.  It  occurs 
at  Las  Chispas,  Sonora,  Mexico,  in  large  masses  and  crystals  with  argentite, 
pyrargyrite  and  polybasite.  It  was  abundant  at  the  Comstock  and  Reese  River, 
Nevada,  and  at  Red  Jacket,  Gunnison  Co.,  and  other  localities  in  Colorado. 
Found  at  the  Saxon,  Bohemian,  Hungarian  and  German  localities  mentioned  under 
proustiteand  pyrargyrite;  also  at  Pachuca,  Mexico;  Arqueros,  Chili,  and  elsewhere. 

POLYBASITE. 

COMPOSITION. — (Ag.Cu^SbSe,  often  with  some  Sb  replaced  by  As. 

GENERAL  DESCRIPTION. — A  soft,  iron-black  mineral,  of  metallic  lustre,  best  known 
in  six-sided  tabular  prisms,  with  bevelled  edges.  In  thin  splinters  it  is  cherry  red  by 
transmitted  light.  Orthorhombic. 

PHYSICAL  CHARACTERS. — Nearly  opaque.  Lustre  metallic.  Color  and  streak, 
black,  but  the  powder  is  red  by  transmitted  light.  H.,  2  to  3.  Sp.  gr.,  6  to  6.2. 
Brittle. 

BEFORE  BLOWPIPE,  ETC. — Fuses  with  spirting.  Gives  off  odor  of  garlic  sometimes, 
but  always  yields  heavy  white  fumes  and  odor  of  sulphur  dioxide,  and  leaves  malleable 
button,  which  in  beads  reacts  for  copper,  or,  if  dissolved  in  nitric  acid,  will  yield  a 
flocculent  white  precipitate  on  addition  of  hydrochloric  acid.  In  closed  tube,  fuses 
very  easily,  but  yields  no  sublimate.  Soluble  in  nitric  acid. 

REMARKS. — A  large  deposit  of  polybasite  at  the  Molly  Gibson  Mine,  Aspen, 
Colorado,  has  been  called  a  primary  replacement  in  limestone.  At  Tonopah,  Nevada, 
argentite  and  polybasite  are  the  principal  ores.  At  Neihart,  Montana,  polybasite 
is  intimately  associated  with  the  galena  and  sphalerite. 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.     391 

In  many  localities,  however,  polybasite  is  part  of  the  secondary  enrichment,  as 
at  Las  Chispas,  Sonora,  Mexico;  Georgetown,  Colorado;  Chafiarcillo,  Chili. 
Occurs  at  Freiberg,  Saxony,  and  Pribram,  Bohemia. 

THE  SILVER  HALOIDS. 

The  compounds  of  silver  with  chlorine  bromine  and  iodine  are 
usually  in  the  " gossan"  of  silver  deposits  or  of  silver  lead  deposits 
and  are  probably  due  to  chiefly  the  precipitating  action  of  surface 
waters  on  silver  sulphate  solutions  though  sometimes  there  is  direct 
replacement  of  argentite  by  cerargyrite.  In  general  the  chloride 
cerargyrite  is  dominant  but  not  always  and  many  so-called  cerar- 
gyrites  are  embolite. 

CERARGYRITE.— Horn  Silver. 

COMPOSITION. — AgCl,    (Ag  75.3  per  cent). 

GENERAL  DESCRIPTION. — A  soft,  grayish-green  to  violet  crust 
or  coating  of  the  consistency  and  lustre  of  horn  or  wax.  Rarely 
in  cubic  crystals. 

Physical  Characters.     H.,  I  to  1.5.     Sp.  gr.,  5  to  5.5. 

LUSTRE,  waxy,  resinous.  TRANSLUCENT. 

STREAK,  shining  white.  TENACITY,  very  sectile. 

COLOR,  pearl  gray  or  greenish,  darkens  on  exposure  to  light, 
becoming  violet,  brown  or  black. 

BEFORE  BLOWPIPE,  ETC. — Fuses  very  easily,  yields  acrid  fumes 
and  a  globule  of  silver.  Rubbed  on  a  moistened  surface  of  zinc 
or  iron,  it  swells,  blackens  and  the  surface  is  silvered,  and  the  min- 
eral is  reduced  to  spongy  metallic  silver.  In  matrass,  with  acid 
potassium  sulphate,  yields  a  globule,  yellow  hot,  white  cold,  and 
made  violet  or  gray  by  sunlight.  Insoluble  in  acids,  soluble  in  am- 
monia. On  coal,  with  oxide  of  copper,  yields  azure-blue  flame. 

SIMILAR  SPECIES. — Bromyrite,  embolite  and  iodyrite  are  most 
easily  distinguished  by  tests  with  acid  potassium  sulphate.  It 
differs  from  argentite  in  color  and  insolubility  in  nitric  acid. 

REMARKS. — It  is  not  abundant  in  Europe  or  Asia  but  is  especially  prominent  in 
the  upper  portions  of  the  "Young"  veins,  p.  382,  famous  localities  being  Pachuca 
and  Las  Chispas,  Mexico;  Chafiarcillo  Caracoles,  Chili,  and  Broken  Hill,  New  South 
Wales.  In  the  United  States  its  most  celebrated  localities  have  been  Poor  Man's 
Lode,  Idaho  and  Horn  Silver,  Utah;  other  noteworthy  localities  being  Leadville, 
Colorado;  Tonopah,  Nevada;  Lake  Valley,  New  Mexico  and  the  chloride  districts 
of  Arizona. 


392  MINER ALOG  Y. 

BROMYRITE. — Bromargyrite. 

COMPOSITION. — AgBr,  (Ag  57.4  per  cent.). 

GENERAL  DESCRIPTION. — Like  cerargyrite,  except  that  the  color  is  bright  yellow  to 
grass  green  or  olive  green.  H.,  2  to  3.  Sp.  gr.,  5.8  to  6.  Usually  found  in  small 
concretions  and  little  altered  by  exposure. 

BEFORE  BLOWPIPE,  ETC. — Like  cerargyrite,  except  that  in  matrass  with  acid  potas- 
sium sulphate  a  little  bromine  vapor  is  evolved,  coloring  the  fluid  salt  yellow,  and  the 
fused  bromyrite  sinks  as  a  dark  red,  transparent  globule,  which,  on  cooling,  becomes 
opaque  and  deep  yellow,  and  when  exposed  to  sunlight  becomes  dark  green. 

REMARKS. — Bromyrite  occasionally  accompanies  cerargyrite  and  at  Chanarcillo, 
Chili,  the  cerargyrite,  bromyrite  and  embolite  are  said  to  have  been  in  closely  the 
proportion  of  the  Cl,  Br  and  I  in  sea  water.  It  occurs  at  Plateros,  Mexico,  and 
Huelgoat,  Brittany,  and  in  this  country  has  been  of  economic  importance  in  Elko 
Co.,  Nevada  and  Sierra  Co.,  New  Mexico. 

EMBOLITE. 

COMPOSITION. — Ag(Q.Br).     Isomorphic  mixtures  of  the  chloride  and  bromide. 

GENERAL  DESCRIPTION. — Intermediate  between  cerargyrite  and  embolite.  Color, 
green  to  yellow,  darkening  on  exposure.  H.,  i  to  1.5.  Sp.  gr.,  5.31  to  5.81. 

BEFORE  BLOWPIPE,  ETC. — The  acid  potassium  sulphate  fusion  is  like  that  of 
cerargyrite  or  that  of  bromyrite,  as  the  bromine  is  small  in  amount  or  plentiful. 

REMARKS. — Embolite  is  said  to  be  more  abundant  than  cerargyrite  in  some  of 
the  Chilian  mines  and  has  been  found  in  important  quantity  in  Lake  Co.,  Colorado; 
the  Pearce  District,  Arizona,  and  Sierra  Co.,  New  Mexico;  Shafter,  Texas;  and 
Broken  Hill,  New  South  Wales. 

IO  D  YRITE. — lodargyrite. 

COMPOSITION. — Agl,  (Ag  46,  I  54  per  cent.). 

GENERAL  DESCRIPTION. — A  yellow  or  yellowish-green,  wax-like  mineral,  occurring 
massive  or  in  thin  flexible  scales  or  in  hexagonal  crystals. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  resinous,  wax-like.  Color,  gray, 
yellow  or  yellowish  green.  Streak  yellow.  H.,  i.  Sp.  gr.,  5.6  to  5.7.  Sectile. 

BEFORE  BLOWPIPE,  ETC. — Fuses  very  easily,  spreads  out  and  gives  pungent  odor. 
In  closed  tube,  fuses  and  becomes  deep  orange  in  color,  but  cools  yellow.  With  oxide 
of  copper,  colors  flame  intense  green.  In  matrass  with  acid  potassium  sulphate, 
yields  violet  vapor  and  deep-red  globule,  which  is  yellow  when  cold  and  not  changed 
by  exposure  to  sunlight. 

REMARKS. — lodyrite  is  found  at  Broken  Hill,  New  South  Wales;  Tonopah, 
Nevada,  and  Sierra  Co.,  New  Mexico.  It  is  more  abundant  in  certain  mines  in 
Chili,  as  at  Algodones. 

THE   GOLD   MINERALS. 

The  minerals  described  are : 

Metal 
Tellurides 


Gold 

Au 

Isometric 

Sylvanite 

(Au.Ag)Te2 

Monoclinic 

Calaverite 

(Au.Ag)Te2 

Krennerite 

(AuAg)Te2 

Orthorhombic 

Petzite 

(Au.Ag)2Te 

Isometric 

Nagyagite 

Au2PbioSb2Te6Si5 

Orthorhombic 

MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     393 

Gold  selenide*  of  unknown  formula  occurs  in  considerable  quantity 
at  Radjang  Lebong,  Sumatra  and  at  Republic,  Washington  (in  a 
gangue  of  fine-grained  quartz).  Gold  amalgam  in  small  amounts 
occurs  occasionally. f 

The  most  important  of  all  gold  ores  is  auriferous  pyrite  and  gold 
also  occurs  in  important  quantities  in  chalcopyrite,  arsenopyrite 
and  stibnite.  Other  minerals  in  which  gold  has  been  included  are 
sphalerite,  smaltite,  niccolite,  tetradymite,  aikinite  and  silicates 
such  as  hornblende,  feldspar,  epidote,  garnet.  It  is  frequently 
alloyed  with  silver,  sometimes  with  bismuth,  mercury  or  palladium. 

ECONOMIC   IMPORTANCE. 

The  gold  production  of  the  world*  for  1915  was  $470,979,890, 
Africa  supplying  46  per  cent,  of  all  and  North  America  28  per  cent. 
The  great  producers  were: 

Transvaal $188,397,707  Rhodesia $18,852,130 

United  States 98,891,000  Mexico 16,975,000 

Australia 44,368,013  Canada 15,875,005 

Russia  and  Siberia 26,750,000  British  India 11,699,385 

The  producers  of  the  remainder,  about  $50,000,000,  were,  in  order  of  importance: 
South  America,  West  Africa,  Japan,  East  Indies,  Central  America,  China,  Madagas- 
car and  France. 

In  this  country  the  leading  regions  were: 

California $23,005,800  Montana $4,763,100 

Colorado 22,191,200  Arizona 4,107,400 

Alaska 16,626,700  Utah 3,494,800 

Nevada 11,314,700  Oregon 1,739,400 

South  Dakota 7.397.4OO  New  Mecixo 1,430,000 

The  percentages  according  to  kind  of  ore  and  method  of  treat- 
ment in  1914  were: 

*Lindgren's  "Mineral  Deposits,"  p.  493.  According  to  Beyschlag,  Vogt  and 
Krusch,  the  selenium  is  associated  with  the  silver  rather  than  the  gold,  p.  589. 
Selenium  is  also  associated  with  the  gold  at  Falun,  Sweden,  and  with  the  silver  and 
gold  deposits  of  Tonopah,  Nevada,  and  is  said  to  constitute  several  per  cent,  of  the 
composition  of  the  Western  Australian  gold  tellurides  (see  Beyschlag,  Vogt  and 
Krusch,  p.  593). 

t  California,  Colombia,  Urals,  Australia,  etc. 

%  Engineering  and  Mining  Journal,  1916,  p.  43. 


394  MINERAL  OGY. 

Placers 25.3                              25.3 

Dry  and  siliceous  ores 66.5 

By  amalgamation 20.9 

By  cyanidation 31.4 

By  chlorination 2 

By  smelting 14.0 

Copper,  lead,  etc.,  ores 8.2 

By  smelting 8.2 


FORMATION    AND    OCCURRENCE    OF    THE    GOLD    DEPOSITS. 

Gold  is  found  in  small  amounts  in  many  igneous  rocks  apparently 
as  a  primary  mineralf  and  in  the  schists  and  gneisses  it  has  occa- 
sionally been  deposited  before  metamorphism  and  intercrystallized 
with  their  silicates.  J 

The  relative  importance  of  the  different  classes  of  deposits — 
the  gravel  deposits  of  each  being  included — are  given§  as 

Witwatersrand  conglomerate  about 35  per  cent. 

Old  gold  veins  about 33 

Young  gold  veins  about 25 

Contact  deposits  about i/S 

Contact  Deposits. 

Contacts  involving  much  gold  are  relatively  rare. 

Reichenstein,  SUesia.\\ — Serpentine  and  limestone  contacts  with 
granite.  The  ore  lollingite  and  arsenopyrite  carrying  gold.  Con- 
tact minerals  diopside,  titanite,  vesuvianite,  apatite  and  fluorite 
present. 

Cable  Mine,  Montana.^ — Free  gold  in  calcite  occurs  at  the  con- 
tact of  limestone  and  quartz  monzonite.  Associates  are  quartz, 
pyrrhotite,  pyrite,  amphibole,  actinolite,  garnet,  magnetite  and 
green  mica. 

Nickel  Plate  Mine,  British  Columbia** — At  the  contact  of 
limestone,  shales  and  quartzites  with  gabbro  and  diorite  there  are 

*  Mineral  Resources  U.  S.,  1914,  p.  862. 

t  Cordilleras  of  Chili.     Aplite  dikes  in  the  Winscott  Mine,  Montana,  etc. 
Beyschlag,  Vogt  and  Krusch  (Truscott),  346.     Embedded  in  fresh  quartz  and 
feldspar  of  a  granite  from  Sonora,  Mex.,  Lindgren,  "Mineral  Deposits,"  p.  10. 
t  Ayrshire  Mine,  Mashonaland,  Lindgren,  p.  13. 
§  Beyschlag,  Vogt  &  Krusch,  p.  646. 
||  Ibid.,  404. 
«[  Ibid.,  697. 
**  "Mineral  Deposits,"  p.  696. 


MINERALS    OF  METALLIFEROUS    ORE  DEPOSITS.      395 

found  free  gold  and  gold-bearing  arsenopyrite,  with  pyrrhotite, 
pyrite,  chalcopyrite,  sphalerite  and  tetradymite.  Associates  are 
garnet  (andradite),  pyroxene,  epidote,  axinite. 

Other  occurrences  with  copper  ores  occur  on  the  eastern  slope  of 
the  Sierra  Madre,  Mexico. 
The  Young  Veins. 

The  characteristics  of  the  young  gold  and  silver  veins  are 
described,  p.  382,  under  silver.  The  examples  there  given  are  of 
mines  with  dominant  silver. 

These  grade  into  veins  rich  in  native  gold  or  gold  pyrite  or 
telluride  of  gold,  that  is,  these  veins  are  connected  with  recent 
igneous  intrusions  and  are  formed  after  the  main  intrusion  by 
gold-bearing  emanations  from  the  interior  magma,  which  fill 
fissures  and  often  also  replace  existing  minerals  and  deposit  their 
load  chiefly  of  quartz,  free  gold,  gold-bearing  pyrite  or  the  gold 
tellurides.  Examples  of  such  deposits  are: 

Goldfields,  Nevada.* — Numerous  fissures  in  highly  altered  rock 
containing  15.73  alunite  in  a  district  covered  by  flows  of  dacite, 
andesite  and  rhyolite.  The  ores  are  native  gold,  and  tellurides 
with  pyrite,  marcasite,  bismuthinite,  etc.,  in  a  flint-like  quartz. 
Silver  is  very  subordinate. 

Transylvania,  Hungary. — (The  most  important  gold  deposits  of 
Europe.)  Andesite  and  dacite  breaking  through  country  rock. 
The  gold  largely  combined  with  tellurium. 

At  Nagyag  there  are  veins  in  the  andesites,  trachytes  and 
dacites  and  in  the  sedimentary  rocks.  Many  veins  are  barren, 
others  carry  sylvanite,  krennerite  and  nagyagite  and  rarely  free 
gold  and  tetrahedrite  in  a  non-crystalline  quartz  gangue.  Still 
others  carry  nagyagite,  sylvanite,  and  other  tellurides  in  a  car- 
bonate gangue  (calcite,  dolomite,  siderite,  rhodochrosite) . 

At  Offenbanya  the  veins  occur  in  a  dacite,  and  some  contain 
nagyagite  and  sylvanite  in  a  gangue  of  quartz  and  calcite. 

Cripple  Creek,  Colorado. — (Tellurides.)  A  red  granitef  broken 
through  by  volcanic  rocks,  the  ore  occurring  in  many  roughly 
radial  narrow  veins  concentrated  within  the  core  of  an  old  volcano 
and  filled  with  a  gangue  of  quartz  and  fluorite  containing  and  often 

*  Lindgren,  "Mineral  Deposits,"  p.  507. 
f  Lindgren,  "Mineral  Deposits,"  p.  489. 


396  MINERALOGY. 

intergrown  with  calaverite  and  sometimes  sylvanite  with  small 
amounts  of  pyrite,  sphalerite,  tetrahedrite,  stibnite  and  molyb- 
denite. Free  gold  is  found  only  in  the  oxidized  zone. 

Western  Australia. — (Tellurides.)  The  various  mines  of  this 
province  have  yielded  over  $600,000,000  in  gold.  At  Kalgoorlie 
the  deposits  are  veins  in  amphibolite  or  contacts  between  amphi- 
bolite  and  granites.  Some  of  the  veins  contain  no  tellurides, 
others  contain  pale  yellow  massive  calaverite  and  nearly  black 
massive,  lustrous  coloradoite  (kalgoorlite) ;  the  pyrite  is  dis- 
seminated in  small  crystals.  In  the  oxidized  zone  there  is  much 
secondary  gold. 

Associated  are  the  common  sulphides  and  occasionally  scheelite 
and  chlorite,  albite,  tourmaline,  calcite,  dolomite,  roscoelite, 
magnetite,  hematite,  etc. 

Sumatra. \ — (Selenides.)  At  Radjang  Lebong  in  a  region  of 
hot  springs  occur  large  gold -silver  veins  in  a  gangue  of  banded 
quartz  and  chalcedony.  The  ore  is  disseminated  finely,  or  if 
rich  appears  as  dark  dendritic  crusts  not  unlike  the  naumannite, 
Ag2Se,  of  Tilkerode.  Analyses  of  the  bullion  show  4.35  per  cent, 
of  selenium. 

The  "Old  "  Gold  Veins. 

In  these  veinsj  the  filling  is  sharply  separate  from  the  country 
rock  and  is.  principally  quartz  carrying  auriferous  pyrite.  There 
is  little  gold  in  the  oxidation  zone,  but  lower  there  may  be  a  zone 
of  enrichment  with  gold  coating  or  filling  cracks  in  the  sulphides 
or  fissures  in  the  quartz.  The  veins  are  rarely  of  great  width  and 
are  usually  simple.  Tourmaline  and  other  silicates  are  more 
common  and  tellurium  is  rare. 

Economically  important  localities  are: 

California.^ — Along  the  west  flank  of  the  Sierra  Nevadas.  The 
mountains,  which  contain  few  veins,  are  principally  massive 
granodiorite.  The  veins  are  generally  in  the  sediments  clustered 
around  smaller  intrusions  and  following  long  lines  of  fracturing 

— : . 

*  These  are  placed  by  Lindgren  under  high  temperature  deposits,  last  cit.,  p.  647, 
but  by  Beyschlag,  Vogt  and  Krusch,  p.  590,  under  the  young  gold  silver  lodes, 
t  Beyschlag,  Vogt  and  Krusch  (Truscott),  p.  589. 
t  Ibid.,  p.  601. 
§  Lindgren,  "Mineral  Deposits,"  p.  530. 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.     397 

such  as  the  "mother  lode"  130  miles  long,  6}^  miles  wide,  the 
"serpentine  belt"  70  miles  long,  etc.  The  ore  is  native  gold, 
always  with  gold-bearing  pyrite,  sometimes  with  gold  tellurides 
(calaverite,  sylvanite,  petzite,  etc.),  and  sometimes  chalcopyrite, 
sphalerite,  galenite,  tetrahedrite.  The  gangue  is  quartz  and  small 
amounts  of  calcite  and  dolomite.  Mariposite,  a  chromium  mica, 
is  common,  roscoelite  and  scheelite  local. 

Victoria,  Australia* — In  several  districts  such  as  Bendigo  and 
Ballarat  slates  and  quartzites  are  intruded  by  quartz  monzonite. 
At  the  folds  of  the  slates  and  sandstone  cavities  develop  which 
have  been  filled  by  quartz,  forming  "saddle-shaped"  masses  carry- 
ing native  gold,  pyrite,  arsenopyrite  and  sometimes  small  amounts 
of  other  sulphides.  The  slates  also  carry  irregular  bodies.  Some- 
what similar  but  small  deposits  are  found  in  the  anticlinal  folds 
of  slate  and  quartzite  in  Nova  Scotia. 

Passagem,  Brazil. — This  great  deposit  is  regarded  as  a  twice- 
shattered  pegmatite  dike.f  The  first  fissures  filled  with  tourma- 
line and  sericite  and  the  later  fissures  with  ore-bearing  solutions. 
The  ore  is  milk-white  quartz  containing  tourmaline,  free  gold 
alloyed  with  bismuth,  gold-bearing  arsenopyrite  and  some  pyrrho- 
tite  and  pyrite.  Associated  are  contact  minerals,  amphibole 
(cummingtonite),  staurolite,  andalusite,  cyanite,  garnet,  biotite 
and  plagioclase. 

Homestake,  South  Dakota. — This  great  deposit,  which  yielded 
in  1914  ore  to  the  value  of  $6,i6o,i6i,{  consists  of  large  lenses§  of 
altered  rock  carrying  the  ore  and  embedded  in  unaltered  clay  slate. 
The  ore  is  fine-grained  free  gold  in  quartz  with  pyrite,  pyrrhotite, 
arsenopyrite,  etc.,  and  much  brownish  amphibole  (cumming- 
tonite) and  some  garnet. 

Beresowsk,  Urals. \\ — Narrow  "ladder"  veins  crossing  decom- 
posed fine  granite  dikes  nearly  at  right  angles  and  extending  a 
little  into  the  surrounding  schists.  The  ore  is  free  gold,  gold-bear- 
ing pyrite  and  small  amounts  of  aikinite,  chalcopyrite  and  galenite. 
The  gangue  is  quartz  with  much  tourmaline. 

*  Lindgren,  "Mineral  Deposits,"  p.  543. 

t  Ibid.,  p.  732. 

J  Mineral  Resources  U.  S.,  1916,  p.  844. 

§  Lindgren,  p.  638. 

|1  Beyschlag,  Vogt  and  Krusch  (Truscott),  p.  629. 


398  MINERAL  OGY. 

Metasomatic  Replacements. 

These  are  comparatively  rare. 

Examples  in  which  the  gold-bearing  emanations  have  replaced 
existing  minerals  as  well  as  filled  fissures  are : 

The  refractory  siliceous  ores  of  Black  Hills,  S.  D.,  replacing 
shaly  limestone.* 

The  ores  of  Delamar,  Nevada,  f  in  which  the  original  gangue  of 
calcite  has  been  replaced  by  cellular  quartz. 

Mt.  Morgan,  Queensland. — A  conical  hill  of  gold-bearing  quartz- 
ite  traversed  by  dikes,  nearly  the  entire  hill  being  workable  gold 
ore.  Ore  is  gold  and  pyrite  in  quartz  of  many  varieties.  In  one 
portion  a  foam-like  siliceous  sinter,  which  floated  on  water,  in 
another  a  crushed  sugar-like  powder,  in  another  solid,  in  others 
stalactitic.  Rickard  regards  it  as  shattered  country  rock  saturated 
with  mineral  solutions  and  in  part  replaced  by  gold-bearing  quartz. 

Southern  Appalachians. — Lindgren  describes  these§  as  "fissure 
veins  and  replacements  in  schists."  Many  stringers  and  lenses 
of  massive  quartz  occur  in  the  crystalline  schists  usually  parallel 
to  the  foliated  structure.  Some  contain  native  gold  with  pyrite 
or  arsenopyrite  and  less  commonly  other  sulphides.  Tellurides 
occur  locally.  The  associates  include  chlorite,  ilmenite,  magne- 
tite, tourmaline,  and  sometimes  gahnite  and  garnet. 

At  Dahlonega,  Ga.,  the  amphibolite  wall  is  altered  to  pale  red 
garnet  carrying  gold  and  dark  green  mica  and  the  gold  is  with 
tetradymite. 

Gold-Bearing  Conglomerates. 

The  original  material  of  a  gold-bearing  conglomerate  may  have 
been  the  detritus  of  gold-bearing  veins  in  which  case  the  gold  is 
usually  in  rounded  grains  or  nuggets  of  free  gold.  Or  the  gold 
may  have  been  of  later  origin  and  have  entered  through  fissures 
or  by  infiltration. 

The  Conglomerates  of  Witwatersrand. — The  origin  of  the  gold  in 
the  conglomerates  of  Witwatersrand  or  "Rand"  in  the  Transvaal 
is  in  doubt. ||  It  is  believed  that  the  mineralization  was  later  than 

*  J.  D.  Irving,  Jour.  Canadian  Institute,  1910,  "Replacement  Ore  Bodies." 

t  Lindgren,  "Mineral  Deposits,"  p.  482. 

J  Beyschlag,  Vogt  and  Krusch  (Truscott),  p.  642. 

§  "Mineral  Deposits,"  p.  634. 

||  Ibid.,  p.  220. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.      399 

the  formation  of  the  conglomerate  and  traceable  to  eruptive 
diabase.  This  deposit,  which  has  yielded  nearly  $2,000,000,000, 
consists  of  pebbles  of  quartz  cemented  by  quartz,  sericite  and 
chlorite  and  with  nodules  and  coatings  of  pyrite  and  specks  of 
crystalline  gold  often  intergrown  with  the  pyrite. 

The  Homestake,  S.  Dakota,  Conglomerate. — This  is  regarded  as 
an  ancient  gold  gravel  resulting  from  the  erosion  of  the  neighboring 
gold  veins. 

Gold  "  Placers  "  or  "  Gravels." 

The  rocks  containing  gold  deposits  are  broken  down  by  weather- 
ing and  the  fragments  and  undissolved  material,  collect  as  sand 
and  gravel  in  the  valleys,  rivers  and  beaches. 

The  gold-bearing  sulphides  yield  free  gold,  iron  hydroxide  and 
soluble  salts;  there  is  some  solution,  possibly  by  ferric  sulphate 
and  redeposition,*  and  some  concentration  by  gravity. 

Practically  every  gold  district  has  its  placer  deposits,  which  are 
commonly  first  worked,  the  important  ones  usually  from  the 
"Old"  gold  veins. 

The  mineral  associates  are  always  characterized  by  relative 
insolubility  and  hardness  and  often  high  specific  gravity — "black 
sand"  (magnetite,  or  ilmenite),  quartz,  garnet,  zircon,  monazite, 
cassiterite,  platinum,  iridosmine,  and  the  so-called  gem  stones. 

The  largest  "placer"  deposits  still  producing  today  are  in 
Alaska,  California  (and  other  American  states,  especially  Montana, 
Idaho  and  Colorado),  British  Columbia,  Siberia,  Australia,  Guiana, 
Colomba,  Belgian  Congo.  Many  other  countries  yield  consider- 
able amounts. 

GOLD.— Native  Gold. 

COMPOSITION.  —  Au,  usually  alloyed  with  Ag,  and  sometimes 
Cu,  Bi,  Rh,  or  Pd. 

'  GENERAL  DESCRIPTION.  —  A  soft  malleable  metal  with  color  and 
streak  varying  from  golden  yellow  to  yellowish  white  according  to 
the  silver  contents.  It  is  found  in  nuggets,  grains,  or  scales,  usually 
so  disseminated  as  to  be  apparent  only  on  assay.  Rarely  in  dis- 
tinct isometric  crystals,  but  more  frequently  in  skeleton  crystals  or 

*  Proof  of  chemically  precipitated  gold  exhibited  in  the  Paris  Exhibition  from 
western  Australia  gravels  included  gold  on  tree  roots,  gold  in  fine  cracks  in  iron  ochre, 
gold  in  stalactites  of  calcite  and  ochre  and  crystals  of  gold  on  secondary  cobalt 
manganese  ore.  Beyschlag,  Vogt  and  Krusch  (Truscott),  p.  1199. 


ij.00 


MINERALOGY. 
FIG.  408. 


Gold,  Butte  Co.,  Cal.     Columbia  University. 

distorted  and  passing  into  wire-like,  net-like,  and  dendritic  shapes. 
Also  occurs  included  in  pyrite,  sphalerite,  galenite,  pyrrhotite,  and 
arsenopyrite. 

Physical  Characters.     H.,  2.5  to  3.     Sp.  gr.,  15.6  to  19.3. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  like  color.  TENACITY,  malleable. 

COLOR,  golden  yellow  to  nearly  silver  white. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  to  a  bright  yellow 
button  insoluble  except  in  aqua  regia.  Any  silver  present  will  sepa- 
rate from  the  solution  as  a  white  curd-like  precipitate.  If  the  solu- 
tion is  evaporated  to  a  thick  syrup  and  diluted  with  water  and 
heated  with  stannous  chloride  it  becomes  purple,  and  a  purple  pre- 
cipitate settles. 

SIMILAR  SPECIES. — Chalcopyrite,  pyrite,  and  scales  of  yellow 
mica  are  mistaken  for  gold,  but  differ  entirely  in  specific  gravity, 
streak,  brittleness,  and  solubility  in  acids. 

THE  GOLD  TELLURIDES.— Calaverite,  Sylvanite,  Krennerite, 
Petzite,  Nagyagite. 

COMPOSITION. — Calaverite  and  the  rarer  sylvanite  and  krenner- 
ite  have  the  same  general  formula  (Au.Ag)Te2:  petzite  is 
(AuAg)2Te  and  nagyagite  Au2PbioSb2Te6Si5. 


MINERALS  OF  METALLIFEROUS   ORE  DEPOSITS.     401 


GENERAL  DESCRIPTION. — The  gold  tellurides  are  in  the  massive 
granular  state  are  of  dull  appearance  and  often  intermixed  with 
pyrite.  Their  colors  range  from  silver  white,  often  tinged  with 
yellow,  steel  gray  and  to  the  nearly  black  of  petzite  and  nagyagite. 
Crystals  are  less  dull  in  lustre.  The  streak  is  like  the  color. 


Calaverite 

Sylvanite 

Krennerite 

Petzite 

Nagyagite 

Hardness  
Specific  gravity  
Color 

2-5 
9.04 
pale  bronze 

1.5  to  2 
7-9  to  8.3 
Steel  gray 

8-35 
Silver  to 

2.5    to  3 
8.72  to  9.02 
Steel  gray 

I       to  1.5 
6.85  to  7.2 
nearly 

yellow 

to  silver 

pale  yellow 

to 
iron  black 

black 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuse  (krennerite  is  said 
to  decrepitate)  to  a  gray  button  which  after  long  heating  yields  a 
light  yellow  bead  of  gold  alloyed  with  silver  which  is  soluble  in 
aqua  regia  with  a  curd-like  white  precipitate,  and  in  the  case  of 
nagyagite  there  will  be  some  yellow  sublimate. 

Rich  powdered  material  (or  the  sublimate)  placed  on  white 
porcelain  touching  a  drop  of  hot  concentrated  imparts  a  violet 
color  to  the  acid. 

In  the  open  tube  yield  white  sublimates  which  wholly  or  in 
part  melt  to  clear  transparent  drops.  Soluble  in  nitric  acid. 

REMARKS. — As  described,  p.  395,  gold  tellurides  occur  chiefly  in  the  "young" 
veins.  Calaverite  is  the  most  common,  both  at  Kalgoorlie  where  it  occurs  massive, 
"and  at  Cripple  Creek,  where  it  is  often  in  complex  crystals.  Sylvanite  is  from  Hun- 
gary, Colorado,  California  and  Oregon.  Petzite  was  in  important  quantities  at  the 
Bassick  Mine,  Colorado,  and  Hungary,  and  nagyagite  in  the  Hungarian  mines. 
Other  localities  are  Calaveras  and  El  Dorado  Co.,  Colorado,  Baker  Co.,  Oregon; 
Kings  Mt.  Mine,  North  Carolina. 

THE   PLATINUM   GROUP. 

The  minerals  described  are: 


Platinum 


Iridium  and  Osmium 


Palladium 


Platinum 

Sperrylite 
Iridium 
Iridosmine 
Palladium 


Pt 

PtAs2 
Ir  Pt 
(Ir.Os) 
Pd 


Isometric 

Isometric 

Isometric 

Hexagonal 

Isometric 


Tests* — Platinum  will  stay  in  the  pan  with  gold  and  will  not 
amalgamate  with  mercury  alone  but  will  float  on  the  surface.     If 

*  For  description  of  methods  of  determining  the  metals  of  the  platinum  group,  see 
papers  by  A.  M.  Smoot  and  Martin  Sch witter.     Eng.  and  Min.  Journ.,  Vol.  99, 
27 


402  MINER  ALOG  Y. 

sodium  is  added  it  will  amalgamate  and  can  later  be  set  free  by 
shaking  up  with  water  until  all  sodium  is  converted  into  sodium 

hydroxide. 

ECONOMIC   IMPORTANCE. 

The  world's  production*  of  these  metals  in  1914  and  1915  is 
estimated  in  troy  ounces  as  follows: 

Crude  Platinum.       —  1914.  1915- 

Russia 241,200  124,000 

Colombia 17,500  18,000 

United  States 5?o  742 

Canada 30  100 

Crude  Iridosmine. 
Tasmania  and  N.  S.  Wales       i  ,248  303 


260,548  143,145 

In  addition  to  this  there  are  considerable!  quantities  recov- 
ered in  the  refining  of  blister  copper  from  ores  in  the  Great  Basin, 
Rocky  Mountains,  California,  and  Alaska,  copper  regions  there 
in  1915  amounted  to  about  8,500  ounces  troy  (Platinum  6,495,  Pla- 
ladium  1,541,  Iridosmine  355,  Iridium  274). 
The  Uses. 

Platinum. — Purified  platinum  is  largely  used  in  laboratory  appa- 
ratus, dentistry  and  jewelry.  An  amount  estimated*  at  43,888 
oz.  in  the  U.  S.  is  in  use  as  a  catalyzer  in  making  fuming  sulphuric 
acid. 

The  so-called  contact  mass  consists  of  asbestos  or  magnesium  sulphate  soaked 
in  a  solution  containing  platinic  chloride  and  then  heated. 

The  metals,  tungsten  and  molybdenum,  have  replaced  platinum 
to  a  great  extent  in  incandescent  lamps,  spark  plug  points  and 
wires  for  the  dental  industry  and  the  improvements  in  platinum 
plating  have  lessened  the  quantities  used  in  jewelry. 

Minor  uses  are  in  photography  for  platinotype  prints,  in  the 
so-called  "oxidizing  of  silver,"  and  in  the  balance  wheels  of 
non-magnetic  watches. 

Iridium. — Platinum  iridium  alloys,  which  are  harder  and  more 

__^ 

p.  700-701,  and  Vol.  97,  p.  1249,  reprinted  in  Mineral  Resources  U.  S.,  1914,  pp.  347, 
and  349- 

*  From  Mineral  Production  U.  S.,  1915,  p.  140. 

t  Mineral  Production  U.  S.,  1915,  p.  139. 

I  Ibid.,  150. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.     403 

resistant  to  acids  than  platinum,  are  used  for  pointing  gold  pens, 
surgical  instruments,  thermo  couples,  draw-plates  for  gold  and 
silver  wire,  knife  edges  in  delicate  balances,  and  for  standard 
weights  and  measures.  The  oxide  is  used  in  porcelain  painting. 
A  process  of  iridium  plating  also  exists. 

Osmium. — Formerly  used  in  filaments  of  electric  lamps,  but  has 
been  replaced  by  tungsten.  A  very  little  is  used  in  medicine  and 
dyeing  and  as  a  stain  in  microscopy. 

Palladium  is  used  in  dental  alloys  as  a  substitute  for  gold  as  a 
catalyzer,  in  soldering  and  whitening  platinum  and  in  coating 
surfaces  such  as  silver  reflectors  of  searchlights,  and  graduated 
circles  of  scientific  instruments. 

Rhodium*  is  used  in  making  crucibles,  dishes,  thermo-couples, 
and  as  a  catalyst. 

No  mineral  chiefly  rhodium  has  been  found.  The  metal  is,  however,  a  noticeable 
constituent  of  the  minerals  of  the  platinum  group.  In  48  analyses  of  platinum  it  is 
recorded  in  45,  ranging  from  11.07  to  0.29  per  cent.  In  12  analyses  of  iridosmine  it 
ranges  from  12.30  to  0.50  per  cent.  In  the  Canadian  sperrylite  there  is  0.72. 
In  the  Brazilian  iridium  6.86  per  cent. 

Platinum,  as  it  occurs  in  nature,  is  always  alloyed  with  iron  and 
other  metals,  from  which  it  must  be  separated  before  it  possesses 
the  peculiar  properties  which  make  it  valuable.  The  native  min- 
eral is  first  treated  with  dilute  aqua  regia,  which  dissolves  out  any 
iron,  gold  or  copper.  Then  concentrated  aqua  regia  is  added  to 
the  residue,  and  the  platinum  and  a  small  amount  of  iridium  are 
brought  into  solution.  After  evaporation  .of  the  excess  of  acid, 
ammonium  chloride  is  added,  the  ammonium-platinic  chloride  be- 
ing formed  and  also  a  small  amount  of  the  iridium  salt.  This  pre- 
cipitate, on  being  heated,  leaves  the  metal,  which  consists  almost 
wholly  of  platinum,  but  also  carries  a  small  amount  of  iridium. 
The  metals  can  be  further  separated,  but  for  many  purposes  this 
alloy  is  preferable  to  the  pure  platinum. 

The  mother  liquor  from  the  platino  chloride  after  the  precipita- 
tion of  the  platinum  contains  the  rhodium  and  palladium  from 
which  the  palladium  is  precipitated  by  potassium  cyanide,  and 
the  rhodium  by  iron  and  elaborate  subsequent  treatment. 

The  insoluble  residue  from  the  crude  ore  contains  most  of  the 
iridium  and  osmium  which  are  recovered  by  fusion  with  zinc  or 
lead  and  later  removal  of  these  metals  by  volatilization  or  solution. 


404  MINERAL  OGY. 

The  residue  may  then  be  roasted  to  distill  off  osmium  tetroxide 
or  boiled  in  nitric  acid  to  dissolve  the  iridium. 

FORMATION  AND  OCCURRENCE  OF  THE  PLATINUM  GROUP  MINERALS. 

The  metals  are  found  in  minute  amounts  in  rocks,  chiefly  com- 
posed of  chrysolite  or  its  alteration,  serpentine,  as  in  the  perido- 
tites  of  Urals,  Sierra  Nevada,  and  Coast  Ranges,  the  dunite  of 
Tulameen  River,  B.  C.,  and  the  serpentine  of  Italy  and  Asia  Minor. 

Magmatic  Segregations  occur  in  the  nickel  pyrrhotite  deposits 
of  Sudbury,  Ontario,  and  Norway.* 

Veins  and  Replacements. 

Platinum  has  been  detected  in  quartz  veins,*  first  at  Antioquia, 
Colombia,  later  at  several  American  localities.  At  the  Boss 
mine,f  Yellow  Pine  District,  Clark  County,  Nevada,  a  quartz 
mass  replacing  dolomite  and  containing  "shoots"  of  chrysocolla, 
etc.,  and  others  of  fine  quartzose  ore  containing  plumbojarosite, 
which  in  turn  contains  gold,  platinum  and  palladium.  The  ore 
averages  per  ton  3.46  oz.  gold,  6.4  silver,  0.7  platinum,  3.68 
palladium.  At  the  Rambler  Mine,  Wyoming,  as  an  arsenical 
compound  of  platinum  and  palladium  in  covellite. 

Sediments. 

In  marine  sediments  overyling  basal  granites  east  of  Cologne, 
Germany,  in  quantities  varying  from  a  trace  to  one  ounce  per  ton. 

Placers  or  Gravels. 

The  economically  important  occurrences  are  gravels  or  placers 
near  areas  of  decomposed  chrysolite  rocks  or  in  rivers  flowing 
from  such  areas. 

Choco,  Colombia. — Platinum  was  discovered  in  1755  in  the  gold- 
bearing  sands  of  Pinto  River,  Choco,  Colombia.  It  is  still  ob- 
tained in  important  quantities  from  the  Pacific  coast  area  between 
the  Cauco  and  Atrato  Rivers. 

Urals. — The  most  important  platinum  placers  of  the  world  are 
near  Nizhni  Tagilsk  on  the  European  slope  of  the  Urals  and 
Goroblagodatsk  on  the  Asiatic  slope.  A  third  smaller  district 
is  also  worked.  The  mineral  is  associated  with  iridosmine  and 
chromite.  These  districts  have  supplied  the  world  but  the  output 

*  Beyschlag,  Vogt  &  Krusch  (Truscott),  1215. 
t  Mineral  Production  U.  S.,  1914,  p.  339. 


MINERALS  OF  METALLIFEROUS   ORE  DEPOSITS.     405 

is  steadily  diminishing  and  the  average  yield  is  now  only  1/20  oz. 
per  ton  gravel  instead  of  Y^  oz.  The  Urals  gravels  are  sometimes 
changed  to  conglomerate. 

Bald  Hills,  Tasmania,  yields  iridosmine  from  placers  and  it  is 
also  found  in  place  in  veins  of  chalcedony  and  opal  in  serpentine. 

The  iridosmine  is  sometimes  coated  with  iron  oxide,  at  other 
times  enclosed  in  chromite.  It  contains  hardly  any  platinum. 

PLATINUM.— Native  Platinum. 

COMPOSITION. — Pt(Fe),  usually  with  small  quantities  of  Rh,  Ir, 
Pd,  Os,  Cu,  and  nearly  always  with  Fe  even  as  high  as  one-sixth 
of  the  whole. 

GENERAL  DESCRIPTION. — A  malleable,  steel-gray  to  white  metal, 
occurring  in  small  grains  and  nuggets  in  alluvial  sands.  Very 
rarely  in  small  cubes. 

Physical  Characters.  H.,  4  to  4,5.     Sp.  gr.,  14  to  19. 
LUSTRE,  metallic.  OPAQUE. 

STREAK,  steel  gray.  TENACITY,  malleable. 

COLOR,  light  steel  gray.  Often  magnetic. 

BEFORE  BLOWPIPE,  ETC. — Infusible  and  unaffected  by  fluxes  or 
any  single  acid.  Soluble  in  aqua  regia. 

SIMILAR  SPECIES. — Heavier  than  silver  and  not  soluble  in  nitric 
acid. 

REMARKS. — Occurs  as  stated,  p.  404,  and  also  in  many  gold  placers  of  California 
and  Oregon  and  sometimes  in  the  beach  sands. 

In  Canada  it  is  found  in  Beauce  County,  Quebec,  and  Tulameen  River,  British 
Columbia.  In  Minas  Geraes,  Brazil  in  gold  sand,  with  palladium,  and  iridosmine. 
It  is  also  found  in  gold  placers  in  Borneo,  New  Zealand  and  New  South  Wales. 

SPERRYLITE. 

COMPOSITION. — PtAs2  (Pt,  52.57;  As,  43.5  per  cent.)  with  some  replacement  of 
platinum  by  rhodium  and  palladium. 

GENERAL   DESCRIPTION. — A   tin-white,   brittle  and   opaque   mineral   of   metallic 

lustre  found  in  minute  cubes  and  octahedra  and  in  grains.     H.,  6  to  7.     Sp.  gr.,  10.60. 

BEFORE  BLOWPIPE,  ETC. — If  rapidly  heated  in  the  open  tube  fuses  easily  with  a 

loss  of  part  of  the  arsenic.     Instantly  fused  if  dropped  on  red  hot  platinum.    In  closed 

tube  unchanged.     Slowly  soluble  in  concentrated  hydrochloric  acid. 

REMARKS. — Occurs  in  small  amount  with  the  nickel  ores  of  Sudbury,  Ontario, 
and  in  the  chalcopyrite  and  covellite  of  the  Rambler,  Mine,  Wyoming.  Has  been 
found  in  Macon  County,  N.  C.,  with  gold  and  rhodolite  and  is  believed  to  exist  in  the 
platinum-bearing  dikes  of  Bunkerville,  Nevada. 


406  MINERAL  OGY. 

IRIDIUM    (PLATIN-IRIDIUM). 

COMPOSITION. — Iridium  alloyed  with  platinum,  palladium,  rhodium,  little  if  any 
osmium. 

GENERAL  DESCRIPTION. — Angular  and  rounded,  slightly  malleable  grains  in 
platinum  deposits  with  specific  gravity  and  melting  point  much  higher  than  platinum. 
Color,  silver  white  with  tinge  of  yellow.  H.,  6  to  7.  Sp.  gr.,  22.6  to  22.8. 

BEFORE  BLOWPIPE,  ETC. — Infusible  and  insoluble  in  all  acids.  Attacked  by 
chlorine  gas. 

REMARKS. — The  rarest  of  platinum  ores.  Found  in  the  Ural  platinum  deposits, 
the  gold  sands  of  Ava,  Burmah.  It  is  reported  also  from  Brazil  and  Tasmania. 

IRIDOSMINE. 

COMPOSITION. — (Ir.Os),  sometimes  with  Rh,  Ft,  etc. 

GENERAL  DESCRIPTION. — A  tin-white  or  gray,  metallic  mineral,  very  hard  and 
heavy,  and  occurring  in  irregular,  flattened  grains  and  hexagonal  plates. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre  metallic.  Color  and  streak,  tin  white 
or  gray.  H.,  6  to  7.  Sp.  gr.,  19.3  to  21. 1.  Rather  brittle. 

BEFORE  BLOWPIPE,  Etc. — Infusible.  May  yield  unpleasant,  pungent  odor.  Insol- 
uble in  acids. 

REMARKS. — Iridosmine  is  found  with  platinum  in  the  Urals;  Choco,  Colombia; 
Bingera,  New  South  Wales;  Victoria;  American  River,  California;  Gunung  Ratus, 
Borneo;  and  Beauce  County,  Quebec. 

PALLADIUM. 

COMPOSITION. — Palladium  with  a  little  platinum  and  iridium. 

GENERAL  DESCRIPTION. — Malleable  grains,  sometimes  radial  fibrous  and  minute 
octahedra  of  light  steel-gray  color.  H.,  4  to  5.  Sp.  gr.,  11.3  to  u.8. 

BEFORE  BLOWPIPE,  ETC. — Melts  more  easily  than  the  other  platinum  metals. 
Heated  in  air  becomes  bluish  on  surface.  Soluble  in  nitric  acid  to  brownish-red 
solution.  Also  soluble  in  concentrated  hydrochloric  or  sulphuric  acids. 

REMARKS. — Found  first  in  the  platinum  from  Choco,  Colombia,  later  in  the 
gold  sands  of  Cornego,  Minas,  Geraes,  Brazil;  and  is  reported  from  the  Antilles  and 
Urals.  Palladium  from  Tilkerode,  Harz,  is  called  "  Allopalladium "  and  considered 
to  be  hexagonal. 

Palladium  occurs  either  as  metal  or  arsenide  in  the  copper  nickel  ores  of  Sudbury 
and  the  slimes  from  these  ores  are  the  chief  commercial  source. 

THE   ALUMINUM   MINERALS. 

THE  minerals  described  are  : 

Fluoride  Cryolite  AlNa3F6  Triclinic 

Oxide  Corundum  A12O3  Hexagonal 

Hydroxides          Bauxite  A12O(OH)4 

Diaspore  AIO(OH)  Orthorhombic 

Gibbsite  A1(OH)3  Monoclinic 

Sulphates  Alunogen  Al2(SO4)3.l8H2O  Monoclinic 

Aluminite  (A1O)2SO4.9H2O  Monoclinic 

Alunite  K(  A1OH)3(SO4)2  +  sH2O       Rhombohedral 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.      407 

Aluminum  is  also  present  in  many  silicates,  the  greater  portion 
being  in  the  feldspars,  feldspathoids,  micas,  aluminous  pyroxenes 
and  amphiboles,  garnet  and  the  clays.  The  phosphates  wavellite 
and  turquois  are  described  elsewhere. 

ECONOMIC   IMPORTANCE. 

The  ores  of  aluminum  are  the  hydroxides,  bauxite,  diaspore, 
gibbsite,  and  the  fluoride,  cryolite.  A  probable  ore  of  the  future 
is  alunite. 

Bauxite  to  the  amount  of  297,041  long  tons  was  produced*  in 
1915,  Arkansas  and  Tennessee  furnishing  272,033  Georgia  and 
Alabama  the  rest. 

Cryolite  to  the  amount  of  about  4,612  tons  was  imported  into 
the  United  States  from  Greenland  in  1914,  and  is  used  as  a  flux 
in  the  manufacture  of  aluminum. 

Alunite  has  been  and  still  is  used  for  the  manufacture  of  alum 
and  in  connection  with  the  first  shipmentf  of  28  tons  of  potassium 
sulphate  in  1915  from  the  treatment  of  Marysvale,  Utah,  alunite, 
the  use  of  the  residual  "filter  cake "  which  is  about  65  per  cent  A12O3 
for  the  manufacture  of  aluminum  becomes  very  probable. 

The  formerly  important  industry  in  manufacturing  alum  from  the  alum  shales 
so  common  in  the  brown  coal  formations  is  of  relatively  small  importance;  the 
soluble  sulphates  were  the  result  of  the  action  of  decomposing  pyrite  on  the 
shales. 

In  1915  this  country  produced||  49,903  short  tons  of  aluminum, 
24,915  o"  alum  and  169,153  of  aluminum  sulphate. 

The  world's  production  of  aluminum  in  1914  is  estimated ^  at 
86,390  metric  tons,  about  one-half  from  the  U.  S. 

United  States 42,210  Canada 6,820 

France 12,000  Austria-Hungary 4,000 

Switzerland 10,000  Norway 2,500 

Great  Britain 8,000  Italy 800 

*  Mineral  Resources  U.  S.,  1914,  p.  183. 

t  Mineral  Resources  U.  S.,  1915,  p.  159. 

J  Ibid.,  1915,  p.  129. 

§  Ibid.,  p.  in. 

1J  Min.  Resources  U.  S.,  1915,  p.  167  and  173. 

Tf  Mineral  Industry,  1914,  p.  189. 


4o8  MINER  A  LOG  Y. 

The  Metallurgy  and  Uses  of  Aluminum. 

j  The  ore  is  heated  with  sodium  carbonate  to  low  redness,  in 
order  to  produce  sodium  aluminate  without  rendering  the  silica 
or  iron  soluble.  On  dissolving  out  the  sodium  aluminate  with 
water  and  passing  carbon  dioxide  through  the  solution,  aluminum 
hydroxide  is  formed,  which  yields  the  oxide  when  heated.  By 
this  mode  of  procedure  most  of  the  iron  and  silicon  are  separated, 
which  would  otherwise  be  reduced  by  the  current  and  alloyed 
with  the  aluminum.  In  a  more  recent  process  the  impurities  in  the 
bauxite  are  removed  by  fusing  the  ore  with  carbon  in  an  electric 
furnace  whereby  iron,  silicon  and  titanium  are  reduced  or  converted 
into  carbides  and  separate  on  top  of  the  aluminum  oxide  formed. 

For  the  production  of  the  pure  metal  the  oxide  is  decomposed 
by  electrolysis  in  a  fused  solvent  which  protects  the  metal  from 
contact  with  oxygen.  The  Hall  and  Heroult  processes  consist  in 
the  electrolysis  of  the  oxide  in  a  fused  bath  of  cryolite  or  the 
mixed  fluorides  of  sodium  and  aluminum.  The  Hall  process  is 
carried  on  in  iron  tanks,  the  bottom  and  sides  of  which  are  thickly 
lined  with  carbon.  The  tanks  serve  as  the  negative  electrodes 
and  are  filled  with  the  cryolite  flux,  to  which  a  little  fluorite  is 
added.  The  positive  electrodes  are  carbon  cylinders,  which  dip 
into  the  electrolyte. 

The  cylinders  are  first  lowered  until  they  touch  the  bottom  of 
the  tank,  and  the  ground  cryolite  is  melted  as  a  result  of  the  poor 
contact.  The  cylinders  are  then  raised,  and  the  current  thenceforth 
passes  through  the  melted  liquid.  The  alumina  is  now  added, 
and  is  immediately  dissolved  by  the  flux  and  decomposed  by  the 
current.  The  metal  settles  at  the  bottom  of  the  bath,  while  the 
oxygen  combines  with  the  carbon  of  the  anode  and  escapes  as 
carbon  dioxide.  The  metal  is  removed  from  time  to  time,  alumina 
is  again  added  and  thus  the  operation  is  continuous. 

Aluminum  is  used  where  lightness,  strength  and  non-corrosive- 
ness  are  desirable,  e.g.,  in  some  scientific  apparatus,  in  fancy  articles, 
to  a  limited  extent  in  cooking  utensils.  It  is  replacing  sheet  copper 
and  zinc,  and  is  used  as  bronze  powder  and  aluminum  leaf  for 
silvering  letters  and  signs.  It  is  of  growing  importance  as  a  sub- 
stitute for  stone  and  zinc  in  lithographing  and  is  used  in  large 
quantities  for  electrical  conductors.  Aluminum  is  especially  son- 
orous and  is  now  used  in  the  Austrian  army  for  drums,  and  the 


MINERALS    OF  METALLIFEROUS    ORE   DEPOSITS.    409 

substitution  of  aluminnm  for  brass  in  the  other  band  instrnments 
is  being  tried. 

Two  interesting  uses  of  aluminum  in  metallurgy  are  :  The  weld- 
ing of  wrought  iron  pipes,  rails  and  steel  castings,  in  place,  by  the 
heat  developed  by  oxidation  of  powdered  aluminum  mixed  with 
oxide  of  iron  (Thermite) ;  the  prevention  of  blow-holes  in  castings 
of  steel,  copper  or  zinc  by  the  addition  of  less  than  one  per  cent,  of 
aluminum  to  the  melted  metal. 

The  alloys  of  aluminum  are  extensively  used,  especially  the  alloy 
with  copper,  known  as  aluminum  bronze,  which  contains  usually 
as  much  as  ten  per  cent,  of  aluminum.  It  is  extremely  tough  and 
is  extensively  applied  in  machinery,  especially  mine  machinery, 
engine  castings,  etc.  The  alloys  with  zinc,  nickel  and  tin  are  also 
of  importance  and  to  some  extent  are  replacing  brass.  The  alloys 
with  zinc  are  malleable  and  ductile  and  when  chilled  possess  a  high 
tensile  strength.  Alloys  with  tungsten  are  also  growing  in  im- 
portance. 

The  great  demand  of  1914  is  said  to  be  due  to  its  use  in  the 
explosive  "ammonal,"  a  mixture  of  nitrate  of  ammonia  and 
powdered  aluminum.  The  burning  of  the  aluminum  expands  the 
explosive  gases. 

Bauxite  with  a  melting  point  of  1,820°  C.  is  not  only  the  source 
of  most  of  the  aluminum  of  commerce  but  is  also  used  in  the 
production  of  alum  and  other  compounds  of  aluminum  used 
extensively  in  dyeing  and  calico  printing.  It  is  also  made  into 
bricks  for  lining  open  hearth  steel  furnaces,  copper  converters 
and  Portland  cement  kilns  and  by  fusion  in  the  electric  furnace 
it  is  made  into  "Alundum"  much  used  in  grinding  steel. 

Cryolite  is  used  in  the  making  of  enamels  for  kitchen  ware  and 
opalescent  glasses. 

The  uses  of  corundum  and  other  described  species  will  be 
mentioned  under  the  species. 

THE   FORMATION  AND    OCCURRENCE   OF  ALUMINUM   MINERALS. 

In  Pegmatites. 

Corundum — in  syenites  and  nepheline  syenites  of  Ontario, 
Canada,  as  15  to  20  per  cent,  of  their  composition,  also  in  syenite 
of  Gallatin  County,  Montana,  and  anorthosite  of  India. 


410  MINERALOGY. 

Cryolite  at  Arksutfiord,  Greenland,  as  central  part  of  coarse 
granitic  pegmatite  carrying  the  common  sulphides  and  marginally 
these  with  wolframite,  cassiterite,  columbite  and  molybdenite. 
An  adjoining  pegmatite  has  the  same  species  but  no  cryolite. 

Magmatic  Segregation. 

Corundum  will  crystallize  directly  from  magmas  such  as  nephe- 
line  syenite  exceptionally  high  in  alumina  and  from  peridotite  or 
other  magnesian  rocks  exceptionally  low  in  alumina.*  In  the 
latter  by  segregation  economic  deposits  may  result  as  in  the  norite 
at  Peekskill,  N.  Y.,  the  amphibolites  of  Chester,  Mass.,  and  the 
"  segregation  lumps  "  near  Mts.  Painter  and  Pitt,  South  Australia. 

In  Contacts. 

Bauxite  is  regarded  by  some  authorities*  as  "  usually  alterations 
of  limestone  in  contact  zones." 

Corundum. — In  limestone  as  with  the  rubies  of  Burma  and  the 
emery  of  Naxos,  Greece,  and  the  adjoining  mainland  of  Asia  Minor. 
The  "contact  veins "|  between  peridotite  and  schists  and  their 
alterations,  the  amphiboles  and  chlorite  schists,  along  the  Appa- 
lachian range  from  Alabama  to  Massachusetts,  especially  in  North 
Carolina,  and  Georgia. 

Formed  by  Exhalations  and  Acid  Solutions. 

Alunite  is  formed  by  action  of  sulphurous  vapors  on  trachyte 
or  other  young,  porous,  orthoclase-bearing  rocks  as  at  Rosita 
Hills,  Colorado;  Marysvale,  Utah;  Goldfields,  Nevada,  where  the 
altered  rocks  enclose  the  gold  deposits;  Cartagena  and  Mazarron, 
Spain,  with  young  gold-silver  veins;  Tolfa,  Rome;  Musaz,  Hun- 
gary; Bullah  Delah,  New  South  Wales;  and  many  other  localities. 

A  large  deposit  at  Kyoquot  Sound,  Vancouver  Island,  is  saidf 
to  be  "of  the  sodic  variety." 

Alunogen. — A  large  deposit  on  Gila  River  near  Silver  City, 
New  Mexico,  occupies  the  crater  of  an  extinct  volcano  and  is 
due  to  action  of  vapors  and  surface  waters  on  the  andesite 
breccia.  § 

*  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  103. 
f  Merrill's  "Non-metallic  Minerals,"  p.  75. 
t  Mineral  Industry,  1914,  p.  40. 
§  Bulletin  No.  315,  U.  S.  Geol.  Survey. 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.     411 

Sedimentary. 

The  usual  aluminous  products  of  rock  decay  in  temperate 
regions  are  the  hydrous  silicates  known  as  clays;  the  hydroxides 
are  rarely  found  in  soil  analyses.  In  tropical  or  sub- tropical 
regions  they  are  frequently  found  as  laterite*  and  bauxite  and 
it  is  probable  that  the  deposits  found  in  temperate  climates  were 
formed  under  different  climatic  conditions,  f 

The  methods  of  formation  are  not  settled  nor  are  all  deposits 
genetically  alike;  some  authorities!  regard  the  bauxite  (and  dias- 
pore)  as  alterations  of  limestone  in  contact  zones  and  to  some 
small  extent  decomposition  products  of  basic  eruptives,  especially 
basalt.  According  to  Lindgren,  the  Gila  River  bauxite  and  certain 
Hawaiian  soils  owe  the  de-silication  of  their  clay  to  sulphuric  acid 
and  sodium  salts, §  while  for  other  regions  quite  different  origins 
are  claimed. 

Arkansas.^ — In  Pulaski  and  Saline  Counties  as  superficial  10  ft. 
deep  beds  over  considerable  areas.  They  rest  on  nepheline  syenite 
and  it  is  thought  that  this  may  have  been  covered  by  salt  or  alka- 
line water,  perhaps  supplied  by  hot  springs  and  that  some  of  the 
dissolved  A12O3  was  precipitated  as  colloid. 

Georgia  and  Alabama. — Pockets  and  irregular  masses  or  curved 
strata  with  clay  and  limonite  in  the  residual  clay  overlying 
dolomite,  occasionally  associated  gibbsite  and  halloysite.  Below 
the  dolomite  is  shale  rich  in  A12O3  and  pyrite.  Many  faults. 
It  is  thought  that  atmospheric  water  percolating  through  the  shale 
decomposed  the  pyrite,  and  the  resulting  acid  solutions  decom- 
posed the  clay  forming  sulphate,  which  dissolved  the  dolomite  and 
was  precipitated  by  it. 

France. — First  at  Les  Vaux  near  Marseilles,  then  in  a  band  almost 
parallel  to  the  Mediterranean  in  Provence  and  Lanquedoc  (Var, 
Herault,  etc.),  in  pockets  in  corroded  limestone.  Attributed  to 
ascending  springs  and  precipitation  by  the  limestone. 

*  Bauxite  and  laterite  are  rocks  rather  than  minerals,  laterite  being  hydroxides 
with  much  iron  and  clay,  transported  and  spread  out  products  of  decomposition  of 
aluminous  rocks;  bauxites,  are  products  formed  in  situ  from  colloidal  material. 

t  Lindgren,  Mineral  Deposits,  p.  330. 

J  Beyschlag,  Vogt  &  Krusch,  p.  103. 

§  Mineral  Deposits,  p.  328. 

|1  Lindgren,  Mineral  Deposits,  p.  329. 


412 


MINERALOGY. 


CRYOLITE.  -Eisstein. 

COMPOSITION.— AlNa3F6.     (Al  12.8,  Na  32.8,  F  54.4  per  cent.). 

GENERAL  DESCRIPTION. — Soft,  translucent,  snow-white  to  color- 
less masses,  resembling  spermaceti  or  white  wax  in  appearance. 
Occasionally  with  groups  of  triclinic  crystals  so  slightly  inclined 
as  to  closely  approach  cubes  and  cubic  octahedrons  in  angle  and 
form. 

Physical  Characters.     H,,  2.5.     Sp.  gr.,  2.95  to  3. 

LUSTRE,  vitreous  or  wax-like.      TRANSLUCENT  or  transparent. 

STREAK,  white.  TENACITY,  brittle. 

COLOR. — Colorless,  white,  brown. 

CLEAVAGE. — Basal  and  prismatic,  angles  near  90°. 

BEFORE  BLOWPIPE,  ETC. — Fuses  very  easily,  with  strong  yellow 
coloration  of  the  flame,  to  a  clear  globule,  opaque  when  cold. 
With  cobalt  solution,  becomes  deep  blue.  In  closed  tube,  yields 
acrid  fumes,  which  attack  and  etch  the  glass.  Soluble  in  acid 
without  effervescence. 

SIMILAR  SPECIES. — Characterized  by  its  easy  fusibility,  and 
fumes  which  attack  glass. 

REMARKS. — Found  at  Ivigtut,  Greenland,  as  described  on  p.  410,  and  in  smaller 
amounts  in  the  Ilmen  Mts.,  Pikes  Peak,  Colorado  and  Yellowstone  Park. 

CORUNDUM.— Sapphire,  Ruby,  Emery. 

COMPOSITION. — A12O3,    (Al  52.9,  O  47.1  per  cent.). 

GENERAL  DESCRIPTION. — With  the  exception  of  the  diamond, 
the  hardest  of  all  minerals.  Occurs  in  three  great  varieties,  which 
are  most  conveniently  described  separately. 


FIG.  409. 


FIG.  410. 


FIG.  411. 


MINERALS   OF  METALLIFEROUS   ORE  DEPOSITS.    413 

CRYSTALLIZATION.  —  Hexagonal.  Scalenohedral  class,  p.  48. 
Axis  c  =  1.363.  Crystals  often  rough  and  rounded.  Second 
order  pyramids  predominate  as  n,  o,  and  w  intersecting  the  vertical 
axis  at  respectively  Jr,  ^c  and  2c.  Unit  rhombohedron  p  and  the 
more  acute  form  /  (2c)  also  occur.  Supplement  angles  nn  —  51  ° 

58';  ^=57°  38';  ww=  56°. 

Optically  — ,  with  rather  strong  refraction  but  weak  double  refrac- 
tion (a  =  1.759;  r=  1767). 

Physical  Characters.     H.,  9.     Sp.  gr.,  3.95  to  4.11. 

LUSTRE,  vitreous  or  adamantine.     TRANSPARENT  to  opaque. 
STREAK,  white.  TENACITY,  brittle  to  tough. 

COLOR,  blue,  red,  green,  yellow,  black,  brown  or  white. 
CLEAVAGE,  rhombohedral,  angle  of  86°  4'. 

BEFORE  BLOWPIPE,  ETC.— Infusible  and  unaltered,  alone  or  with 
soda,  or  sometimes  improved  in  color.  Becomes  blue  with  cobalt 
solution  at  high  heat.  Insoluble  in  acids  and  only  slowly  soluble 
in  borax  or  salt  of  phosphorus. 

Varieties. 

Sapphire  or  Ruby.  —  Transparent  to  translucent,  sometimes  in 
crystals  and  of  fine  colors  —  blues,  reds,  greens,  yellows,  etc. 

Adamantine  Spar  or  Corundum.  —  Coarse  crystals  or  masses, 
with  cleavage  86°  and  parting  57°,  or  granular,  slightly  translu- 
cent, and  usually  in  some  blue,  gray,  brown  or  black  color. 

Emery. — Opaque,  granular  corundum,  intimately  mixed  with 
hematite  or  magnetite,  usually  dark-gray  or  black  in  color. 

REMARKS. — The  occurrence  of  corundum  as  direct  crystallization  from  magma 
and  of  deposits  in  pegmatites  and  as  segregations,  and  contact  veins  have  been 
pointed  out,  pp.  409,  410.  The  usual  connection  is  with  peridolites  gabbros  norites 
and  similar  rocks  and  their  alterations  carrying  chrysolite  or  in  synenitic  rocks, 
less  frequently  in  limestones  and  dolomites.  Prominent  localities  have  already  been 
mentioned. 

USES. — The  use  as  gems  is  discussed  later.  Adamantine  spar  and  emery  are 
important  abrasive  materials,  and  thousands  of  tons  are  used  in  grinding  and 
polishing  glass,  gems  and  metals. 

BAUXITE.    Laterite. 

COMPOSITION. — *A12O3,  2H2O,  this  fitting  fairly  the  French 
deposits,  whereas  the  Georgia  deposits  are  closely  gibbsite,  A12O3, 

*  Beyschlag,  Vogt  &  Krusch  (Truscott),  p.  359. 


414  MINERALOGY. 

3H2O,  and  the  hydroxide  of  metasomatic*  origin  is  stated  to  be 
chiefly  diaspore,  A12O3,  H2O.  Bauxite  is  rather  a  rock  of  colloidal 
origin  than  a  mineral  and  may  be  regarded  as  a  mixture  of  dias- 
pore and  gibbsite.  TiO2  is  present,  up  to  4  per  cent,  and  some- 
times vanadium. 

GENERAL  DESCRIPTION. — Usually  pisolitic  masses  or  porous 
to  compact,  earthy  and  clay-like.  Color,  white,  gray,  cream,  or, 
if  ferruginous,  will  be  yellow,  brown  or  red. 

FIG.  413. 


Bauxite,  Bartow  County,  Ga.     U.  S.  National  Museum.     . 

Physical  Characters.     H.,  i  to  3.     Sp.  gr.,  2.4  to  2.5. 
LUSTRE,  dull  or  earthy.  OPAQUE. 

STREAK,  like  color.  TENACITY,  brittle. 

COLOR,  white,  red,  yellow,  brown  or  black. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  Becomes  deep  blue  with 
cobalt  solution,  and  may  become  magnetic  in  reducing  flame.  In 
closed  tube  yields  water  at  high  heat.  Soluble  with  difficulty  in 
hydrochloric  acid. 

REMARKS. — In  addition  to  the  deposits  mentioned  on  p.  411,  deposits  of  less 
moment  occur  in  Carniola,  Austria;  Italy,  Ireland,  and  the  Pyrenees.  Extensive 
"laterite"  deposits  occur  in  India  and  elsewhere,  which  usually  carry  much  iron  and 
clay. 


MINERALS    OF  METALLIFEROUS   ORE   DEPOSITS.     415 

DIASPORE. 

COMPOSITION.— AIO(OH),  (A12O3  85.1,  H2O  14.9  per  cent.). 

GENERAL  DESCRIPTION. — Thin,  flat,  orthorhombic  prisms,  foliated  masses  and  thin 
scales.  When  pure,  it  is  transparent  and  white  or  pinkish  in  color.  When  impure,  it 

is  often  brown 

PHYSICAL  CHARACTERS. — Transparent  to  nearly  opaque.  Lustre,  pearly  and  vitre- 
ous. Color,  gray,  white,  pink,  yellow,  brown.  Streak,  white.  H.,  6.5  to  7.  Sp.  gr., 
3-3  to  3-5-  Very  brittle.  Cleaves  into  plates. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  Usually  decrepitates.  With  cobalt  solution, 
becomes  deep  blue.  In  closed  tube,  yields  water  at  high  heat.  Insoluble  in  acids. 

SIMILAR  SPECIES. — Distinguished  by  its  hardness,  cleavage  and  decrepitation. 

REMARKS. — Occurs  with  corundum  and  its  associates  at  Chester,  Mass.,  also  with 
bauxite  and  laterite.  At  Remez,  Hungary,  occurs  at  contact  with  limestone. 

GIBBSITE. 

COMPOSITION.— Al  (OH  )>,  (A12O8  65.4,  H2O  34.6  per  cent.). 

GENERAL  DESCRIPTION. — Best  known  as  a  white  or  nearly  white  mineral,  usually 
occurring  in  small  stalactities  (Fig.  205)  or  thin  smooth  crusts,  with  fibrous  internal 
structure.  Rarely  in  small  monoclinic  crystals.  The  great  deposits  of  "bauxite" 
in  Georgia  are,  however,  chiefly  gibbsite. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  faint  vitreous.  Color,  white 
greenish,  reddish,  yellow.  Streak,  white.  H.,  2.5  to  3.5.  Sp.  gr.,  2.38. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  exfoliates,  glows  and  becomes  white.  With 
cobalt  solution  becomes  deep  blue.  In  closed  tube  yields  water.  Soluble  in  hydro- 
chloric or  sulphuric  acid. 

REMARKS. — Rare  as  pure  material,  plentiful  in  bauxite  and  laterite.  The  pure 
mineral  is  found  with  corundum  in  Asia  Minor,  in  elaeolite  syenite  in  Norway  and 
in  small  quantity  at  Richmond  and  Lenox,  Mass.,  and  Dutchess  and  Orange  counties, 
N.  Y. 

ALUMINITE. 

COMPOSITION.  —  (AlO^SO^HjO,  (A12O3  29.6,  SO8  23.3,  H,O  47.1  per  cent). 

GENERAL  DESCRIPTION. — Usually  found  in  white  rounded  or  irregular  masses  of 
chalk-like  texture  and  peculiar  harsh  feeling. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  dull  or  earthy.  Color  and  streak,  white. 
H.,  l  to  2.  Sp.  gr.,  1.66.  Meagre  to  the  touch  and  adheres  to  the  tongue. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  In  closed  tube  yields  much  acid  water. 
With  cobalt  solution  becomes  deep  blue.  Easily  soluble  in  acid. 

REMARKS. — Found  in  clay  beds  at  Halle,  Germany,  and  at  Brighton,  England, 
filling  a  three-foot  cleft  in  the  chalk.  Other  localities  in  France  and  Bohemia. 

ALUNOGEN. 

COMPOSITION.— A12(S04)3  +  18  H2O,  (A12O3 15.3,  SO3  36.0,  H2O48.7  per  cent.). 

GENERAL  DESCRIPTION.— A  delicate  fibrous  crust  of  white  or  yellow  color.  Some- 
times massive.  Tastes  like  alum. 

PHYSICAL  CHARACTERS.— Translucent.  Lustre,  vitreous  or  silky.  Color,  white 
yellowish  or  reddish.  Streak,  white.  H.,  1.5  to  2.  Sp.  gr.,  1.6  to  1.8.  Taste,  like 
alum. 


41 6  MINER ALOG  Y. 

BEFORE  BLOWPIPE,  ETC. — Melts  in  its  own  water  of  crystallization,  but  becomes 
infusible.  It  is  colored  deep  blue  by  cobalt  solution.  In  closed  tube  yields  much 
acid  water.  Easily  soluble  in  water. 

REMARKS. — Formed  by  action  of  sulphuric  acid  of  decomposing  sulphides  upon 
aluminous  shales.  Also  formed  during  volcanic  action. 

The  large  deposit  near  Silver  City,  New  Mexico,  has  been  mentioned  on  p.  410. 

ALUNITE.  — Alum  Stone. 

COMPOSITION.  —  K(A1OH)3(SO4)2  +  3  H20,  (A1208  37.0,  K2O 
11.4,  SO3  38.6,  H2O  13  per  cent). 

GENERAL  DESCRIPTION. — Occurs  fibrous  and  in  tabular  to  nearly 
cubic  rhombohedral  crystals,  or  so  intermixed  with  a  siliceous 
material  as  to  form  a  hard  granular  and  nearly  white  rock. 

Physical  Characters.      H.,  3.5  to  4.     Sp.  gr.,  2.58  to  2.75. 

LUSTRE,  vitreous.  TRANSPARENT  to  nearly  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  grayish  or  reddish. 

BEFORE  BLOWPIPE,  ETC. — Infusible  and  decrepitates.  With  cobalt 
solution  becomes  deep  blue.  With  soda  infusible,  but  the  mass 
will  stain  silver.  In  closed  tube  yields  water  at  a  red  heat.  Im- 
perfectly soluble  in  hydrochloric  or  sulphuric  acid. 

The  specimen  may  be  boiled  in  water  or  acid  to  remove  soluble 
sulphates,  then  heated  to  redness,  again  boiled  in  water,  the  clear 
liquid  tested  by  addition  of  BaCl2. 

REMARKS. — The  formation  and  principal  occurrences  are  stated  on  p.  410,  and 
its  uses  on  p.  418. 


CHAPTER  XIX. 

MINERALS  IMPORTANT  IN  THE  INDUSTRIES  AND  NOT 
ALREADY   DESCRIBED. 

In  this  division  the  minerals  are  rather  of  chemical  than  of 
metallurgical  importance,  although  the  line  is  difficult  to  draw. 
So  far  as  possible  the  minerals  used  as  sources  of  compounds  of  a 
particular  element  are  grouped  together. 

It  is  to  be  noted  that  the  minerals  are  for  the  most  part  products 
of  weathering  of  the  rocks  and  deposited  from  weathering  solu- 
tions, rather  than  separations  from  magma  or  magmatic  waters. 

THE   POTASSIUM   MINERALS. 

THE  minerals  described  are  : 


Chlorides 

Sylvite 

KC1 

Isometric 

Carnallite 

KCl.MgCl26H20 

Orthorhombic 

Kainite 

KCl.MgSO4.3H2O 

Monoclinic 

Sulphates 

Ka  Unite 

K  Al(SO4)2.i2H2O 

Isometric 

Nitrate 

Nitre 

KN03 

Orthorhombic 

In  addition  to  these,  potassium  is  a  constituent  of  many  silicates, 
such  as  orthoclase,  muscovite  and  leucite.  It  is  also  found  in 
solution  in  many  brines. 

ECONOMIC   IMPORTANCE. 

Potash  salts  to  the  amount  of  306,000  tons  were  imported  in 
1913.  In  1914  this  had  diminished  to  243,000  and  in  1915  to 
85,000  tons*  valued  at  $3,765,224. 

The  imports  in  pounds  of  different  salts  were: 

1914-  1915. 

Carbonate  of,  crude 9,326,899  5.386,719 

Caustic,  not  including  refined 7,284,176  2,032,319 

Cyanide  of 4*7. 139  871,871 

Chloride  of 371,521,920  2,296,606 

Nitrate  of,  saltpeter,  crude 2,230,528  6,855 

Sulphate  of 80,447,360  25,415,040 

All  other 14,590,437  7,502,806 


Total 485,818,459  170,555.450 

*  Mineral  Industry  of  U.  S.,  1915,  p.  96. 
28  417 


41 8  MINERALOGY. 

As  one  effect  of  the  European  war  this  country  has  been  forced 
to  search  for  and  utilize  other  sources  for  potash  than  the  Stassfurt 
salts  and  in  1915  potash  salts  to  the  value  of  $342,000  were 
obtained*  from  domestic  sources,  such  as: 

By-product  potash  from  the  cement  manufacture. 

Potassium  sulphate  from  alunite  of  Maryvale,  Utah. 

Dried  kelp. 

By  evaporation  of  water  from  Jesse  Lake,  Nebraska. 

The  usesf  of  the  potassium  salts  and  the  quantities  used  are 
indicated  by  the  importations  for  the  month  of  February,  1914: 

Fertilizer  salts:  Other  potash  salts: 

Long  Tons.  Pounds. 

Kainite 72,008  Carbonate  of  potash.  .  1,674,685 

Manure  salts 12,451                         Caustic  potash 520,166 

Sulphate  of  potash 5,098  Nitrate  of  potash.  .  .  .  22,699 

Chloride  of  potash 13,172  Cyanide  of  potash.  ...  5,641 

Other  potash  salts.  ...  638,112 

The  carbonate  of  potash  is  used  in  glass-making,  the  cyanide  in 
metallurgy,  the  nitrate  in  explosives,  the  sulphate  and  the  chloride 
in  fertilizers.  Other  large  amounts  are  used  in  making  soap, 
matches,  in  photography  and  pharmacy. 

While  the  search  for  the  solid  deposits  similar  to  those  of  Stassfurt 
and  for  deposits  of  nitrate  of  commercial  importance  has  not 
been  successful  other  saline  lakest  rich  in  potash  salts  are  being 
equipped  for  extraction,  such  as  Searles  Lake,  California;  Owens 
Lake,  California;  Great  Salt  Lake,  Utah. 

Alunite,  p.  416,  has  been  successfully  treated§  at  Marysvale, 
Utah.  It  is  crushed,  roasted,  digested  with  water  and  potassium 
sulphate  obtained.  The  filter  cake  is  about  65  per  cent.  A12O3 
and  the  K2SO4  over  95  per  cent.  pure. 

Methods  have  been  described  and  patented  for  production  of 
potassium  salts  from  orthoclase,  leucite  and  sericite  or  white 
muscovite.  It  is  said  the  products  are  necessarily  low  grade.  j| 

*  Ibid.,  p.  95. 

t  Ibid.,  p.  95. 

t  Mineral  Resources,  U.  S.,  1915,  pp.  101-103. 

§  Ibid.,  p.  no. 

||  Ibid.,  p.  95- 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        419 
FORMATION   AND    OCCURRENCE. 

The  crust  of  the  earth  contains,  it  is  estimated,  2.33  per  cent,  of 
potassium,  very  largely  in  the  great  silicates,  orthoclase,  muscovite 
and  leucite  and  in  the  products  resulting  from  their  decomposition. 
It  is  necessary  to  plant  life  and  is  present  in  all  soils,  being,  as 
stated  on  p.  244,  at  the  decomposition  of  the  rocks  carried  off  to  a 
much  less  extent  than  sodium  by  the  solutions,  but  adsorbed  by 
colloidal  matters 'in  clay  and  soil  and  often  recombined  to  sericite 
(white  muscovite).  The  portion  that  does  reach  the  sea  is  again 
lessened  by  seaweed  and  even  in  land-locked  basins  after  the 
deposition  of  the  less  soluble  calcium  and  sodium  salts  is  rarely 
deposited  but  remains  in  the  mother  liquor  or  bitterns.  Some 
Michigan  brines  contain  up  to  3  to  5  gm.  per  liter.  One  at  Fair- 
port  Harbor,  Ohio,  ran  7.4  KC1. 

Under  the  Ochsenius  "bar"  theory,  p.  423,  the  dense  solutions 
before  the  separation  of  the  potassium  and  magnesium  salts 
reach  the  bar  level  and  the  "bitterns"  escape  to  the  sea. 

In  rare  instances,  as  at  Stassfurt,  Germany,  p.  225,  from  peculiar 
geological  conditions  these  residual  salts  (Abraumsalze)  are  de- 
posited principally  as  carnallite  and  kainite,  sylvite  being  sub- 
ordinate. 

Smaller  deposits  exist  in  Upper  Alsace,  Tyrol,  Kalusz,  Galicia, 
and  India  and  valuable  deposits  have  been  found  in  mining  salt 
near  Suria,  south  of  Cardona,  near  Barcelona,  in  northeastern 
Spain. 

Nitre  deposits  are  numerous  but  not  generally  large — an  exten- 
sive layer  exists  in  the  soda  nitre  region  of  Tarapaca,  Chili,  and 
small  deposits  in  Arizona,  Idaho  and  elsewhere. 

SYLVITE. 

COMPOSITION.— KC1,    (K  52.4  per  cent.). 

GENERAL  DESCRIPTION. — Colorless,  transparent  cubes  or  white  masses,  which  look 
like  common  salt  and  have  somewhat  similar  taste.  Absorbs  moisture  and  becomes 
damp. 

PHYSICAL  CHARACTERS. — Transparent  when  pure.  Lustre,  vitreous.  Color,  color- 
less white,  bluish,  reddish.  Streak,  white.  H.,  2.  Sp.  gr.,  1.97  to  1.99.  Taste,  like 
salt.  Cleavage  in  cubes. 

BEFORE  BLOWPIPE,  ETC. — Fuses  very  readily,  coloring  flame  violet.  If  added  to  a 
salt  of  phosphorus  and  copper  oxide  bead,  the  flame  is  colored  azure  blue.  Soluble  in 
water  and  acids. 


420  MINERALOGY. 

CARNALLITE. 

COMPOSITION.— KCl.MgCl  +  6H.jO  (K  14.1  percent.). 

GENERAL  DESCRIPTION.  —  A  massive  and  somewhat  granular  mineral  occurring  in 
beds  or  strata  at  the  Stassfurt  potash  salts  deposit  of  Germany.  Seldom  found  in 
crystals. 

PHYSICAL  CHARACTERS.  —  Translucent  to  transparent.  Lustre,  sub- vitreous.  Color, 
white,  brownish  and  reddish.  Streak,  white.  H.,  i.  G=i.62.  Taste,  salty  and 
bitter. 

BEFORE  BLOWPIPE,  ETC.  —  Same  as  for  sylvite.     Very  deliquescent. 

USES.  —  Is  the  chief  source  of  the  manufactured  potash  salts  of  commerce  which  are 
so  largely  used  as  fertilizers.  It  is  simply  dissolved  in  water  and  the  potassium  chloride 
crystallized  out  at  the  proper  temperature. 

KAINITE. 

COMPOSITION.  —  MgSO4.KCl  +  3H2O. 

GENERAL  DESCRIPTION.  —  White  to  dark  red  granular  crusts 
with  salty  taste,  also  tabular  and  prismatic  monoclinic  crystals. 

Physical  Characters.     H.,  2.5-3.     Sp.  gr.,  2.05-2.2. 

LUSTRE,  vitreous.  TRANSPARENT  to  translucent. 

STREAK,  colorless.  TASTE,  salty  and  astringent. 

COLOR,  white  to  reddish  white,  and  colorless. 

BEFORE  BLOWPIPE,  ETC.  —  Easily  fusible,  coloring  the  flame 
violet.  After  fusion  on  charcoal  in  reducing  flame  the  moistened 
mass  will  stain  bright  silver.  Soluble  in  water. 

KALINITE.  —  Potash  Alum. 

COMPOSITION.  —  KAl(SO4)2-f  i2H2O,  (K2Og.g,  AlaO8 10.8,  SO333.8,  H2O45.5 
per  cent.). 

GENERAL  DESCRIPTION.  —  Natural  alum  with  the  peculiar  taste,  occurring  as  a  white 
efflorescence  on  argillaceous  minerals.  Usually  fibrous,  or  as  mealy  crusts,  or  compact. 

PHYSICAL  CHARACTERS.  —  Transparent  or  translucent.  Color,  white.  Lustre, 
vitreous.  Streak,  white.  Taste,  astringent.  Tenacity,  brittle.  H.,  2.5.  Sp.  gr.,  1.75. 

BEFORE  BLOWPIPE,  ETC. — On  heating,  becomes  liquid,  yields  water,  and  finally 
swells  to  a  white,  spongy,  easily-powdered  mass,  which  is  infusible,  but  colors  the  flame 
violet.  With  cobalt  solution,  becomes  deep  blue  on  heating.  Soluble  in  water. 

REMARKS. — A  white  efflorescence  on  pyritiferous  clays  or  clay  slates  arid  a 
sublimation  product  of  burning  coal  fields  and  volcanoes. 

NITRE.— Saltpetre. 

COMPOSITION.— KNO3,    (K2O  46.5,  N2O5  53.5  per  cent). 

GENERAL  DESCRIPTION. — White  crusts,  needle-like,  orthorhom- 
bic  crystals  and  silky  tufts,  occurring  in  limestone  caverns  or  as 
incrustations  upon  the  earth's  surface  or  on  walls,  rocks,  etc.  Not 
altered  by  exposure. 


MINERALS   IMPORTANT  IN   THE  INDUSTRIES.        421 

Physical  Characters.     H.,  2.  Sp.  gr.,  2.09  to  2.14. 
LUSTRE,  vitreous.  TRANSLUCENT. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  colorless,  white,  gray.  TASTE,  salty  and  cooling. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  easily,  deflagrates 
violently  like  gunpowder,  colors  the  flame  violet.  Soluble  in 
water, 

REMARKS. — Occurs  as  an  efflorescence  in  soils  containing  excrement  as  in  India, 
Egypt,  Algeria,  Persia,  Spain.  Sometimes  occurs  lining  the  walls  of  caves  in  lime- 
stone as  in  Kentucky,  Tennessee,  France  and  Germany. 

THE    SODIUM   MINERALS. 

The  minerals  described  are : 

Chloride  Halite  NaCl  Isometric 

Sulphate  Mirabilite  Na2SO4.loH2O  Monoclinic 

Nitrate  Soda  Nitre         NaNOs  Hexagonal 

Carbonate         Trona  Na2CO3.HNaCO3.2H2O  Monoclinic 

Sodium  is  an  important  constituent  in  plagioclase  nephelite, 
sodalite  and  other  silicates,  and  in  such  minerals  as  cryolite, 
ulexite  and  borax. 

ECONOMIC    IMPORTANCE. 

The  only  sodium  salt  produced  in  quantity  in  the  United  States 
is  halite,  of  which  the  production  in  1915*  was  5,352,409  short 
tons  produced  by  fourteen  states,  nearly  half  coming  from  Michi- 
gan and  New  York  and  about  one  fifth  from  Ohio,  Kansas, 
Louisiana  and  California  in  the  order  named. 

Mirabilite  from  Wyoming  and  the  Great  Salt  Lake  and  trona 
from  Nevada  and  California  in  comparatively  small  amounts  are 
obtained. 

Soda  nitre  was  importedf  in  1914  to  the  amount  of  620,533 
tons,  as  well  as  many  manufactured  salts.  Those  imported  in 
excess  of  500  tons  in  1914  being: 

Sulphide 1,265  Nitrite 922 

Prussiate 1,147  Phosphate 682 

Ash 1,114  Silicate 523 

*  Mineral  Resources  U.  S.,  1915,  p.  265. 
f  Mineral  Industry,  1914,  p.  675. 


422  MINERAL  OGY. 

In  this  country  about  one  fifth  of  the  salt  is  mined  or  obtained 
from  deep  shaft  mines*  or  open  cuts  as  rock  salt,  the  rest  is  ob- 
tained by  evaporation  of  the  artificial  or  natural  brines,  bitterns, 
and  sea  water,  using  as  heat  the  sun's  rays  or  an  artificial  source. 

Probably  one  half  the  halite  is  used  for  culinary  and  preservative 
purposes,  over  1,000,000  tons  per  year  are  converted  into  sodium 
and  chlorine  compounds,  chief  among  which  aref  sodium  carbonate 
and  bicarbonate,  caustic  soda  and  bleaching  powder. 

About  2,000  tons  of  metallic  sodium  are  made  in  the  United 
States  yearly  by  the  Castner  process  and  until  recently  8,000  to 
9,000  tons  of  sodium  cyanide  for  metallurgical  purposes. 

Minor  uses  are  in  glazing  pottery  and  in  many  metallurgical 
processes  and  the  manufactured  carbonate  and  caustic  soda  have 
their  large  uses  in  glass  and  soap  making,  bleaching,  etc. 

Soda  nitre  is  used  in  the  manufacture  of  nitre  for  gunpowder, 
in  the  production  of  nitric  acid,  but  chiefly  for  fertilizing  purposes. 

FORMATION   AND    OCCURRENCE    OF   SODIUM    SALTS. 

The  economically  important  sodium  compounds  which  occur 
as  minerals  are  all  deposits  from  weathering  solutions  assisted  in 
the  case  of  soda  nitre  probably  by  organic  deposits. 

Halite  occurs  in  beds  varying  from  a  few  feet  to  over  three 
thousand  feet  in  thickness,  in  all  geologic  agesj  except  the  Archaean, 
commonly  underlain  by  gypsum  and  anhydrite,  sometimes  alter- 
nating with  clay,  gypsum,  anhydrite,  marl  and  dolomite.  It 
occurs  also  in  nearly  all  water,  from  infinitesimal  quantities  to 
strong  brines,  and  as  incrustations  on  high  planes  in  dry  regions. 

The  solids  in  seawater  average  3.5  per  cent.  The  evaporation 
of  300  feet  would  only  mean  a  bed  of  less  than  six  feet  thick. 
As  it  is  difficult  to  imagine  a  steady  subsidence  sufficient  to 

*Salt  mines  are  worked  in  Livingston  County,  New  York;  near  Detroit,  Mich- 
igan; in  Ellsworth  and  Rice  Counties,  Kansas,  and  on  Weeks  and  Avery  Islands, 
Louisiana. 

t  Sodium  sulphate  (salt-cake)  is  first  made  and  from  this  caustic  soda,  carbonate, 
bicarbonate,  etc. 

tWeinschenk  gives  Silurian  "Pendschab,"  Carboniferous,  England  and  North 
America;  Dyas,  north  and  middle  Germany;  Triassic,  Wurtemberg  and  the  Alps; 
Jurassic,  Bex,  Switzerland;  Cretaceous,  Algiers;  Tertiary,  Carpathians,  Spain,  Sicily; 
Armenia,  Persia.  "  Grundziige  des  Gesteinskunde,"  243. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        423 

explain  deposits  1 ,000  to  3,000  ft.  thick  the  Bar  theory  of  Ochsenius* 
is  generally  accepted.  For  the  dissolved  constituents  to  separate 
there  is  needed  a  concentration  of  the  solution,  usually  a  land- 
locked basin  with  a  shallow  bar  between  it  and  the  sea,  the  surface 
layers  sinking  as  they  become  denser. 

Michigan,  New  York,  Ohio  and  Pennsylvania  produce  salt 
derived  from  "the  evaporation  of  some  great  sea."  At  least  six 
successive  periods  of  evaporation  took  place  and  each  bed  of  salt 
is  underlain  by  one  or  more  of  dolomite  anhydrite  and  marl. 

Enormous  dome-shaped  deposits  of  very  pure  rock  salt  sur- 
rounded on  all  sides  by  clay  occur  in  Louisiana.  On  Weeks 
Island  it  is  at  least  4,000  ft.  thick  and  very  pure.  At  Petite  Anse 
there  are  2,263  feet  °f  Pure  salt>  then  7°  ^eet  °f  foreign  matter,  then 
more  salt  to  an  unknown  depth.  Curiously,  they  are  overlain  by 
enormous  beds  200  to  600  feet  thick  of  gypsum  and  anhydrite 
or  oil-bearing  limestone.  The  conditions  of  formation  are  not 
understood,  f 

In  the  drier  western  states  halite  is  found  as  at  Salton,  California, 
in  crusts  10-20  inches  thick,  then  mud,  then  another  salt  crust 
and  the  whole  over  hard  clay.  Similar  deposits  occur  in  North 
Africa. 

Famous  foreign  salt  deposits  are  Wieliczka,  Poland;  Cheshire, 
England;  Salzburg,  Tyrol. 

The  Sulphates  of  Soda. 

Like  halite,  the  sulphates  of  soda  are  derived  from  the  weather- 
ing solutions  but  rather  in  inland  "lakes"  lacking  much  calcium 
or  magnesium.  Little  is  formed  in  marine  basins,  the  sulphuric 
acid  being  there  deposited  as  gypsum,  anhydrite,  kieserite,  etc. 

As  with  the  sulphates  of  lime,  p.  440,  strong  salt  solutions 
dehydrate  therefore  the  hydrous  sulphate  mirabilite  is  deposited 
from  pure  solution,  while  the  anhydrous  sulphate  thenardite 
deposits  in  presence  of  much  halite. 

*  "Die  Bildung  der  Steinsalzlager,"  Halle,  1877. 

The  reason  for  the  non-evaporation  of  the  residual  salts  is  that  the  dense  solu- 
tions in  time  reach  the  level  of  the  bar  and  the  residual  bittern  escapes.  The  Gulf 
of  Karaboghaz,  east  side  of  Caspian  Sea,  is  instanced  by  Clarke. 

"Data  Geochemistry,"  p.  211.     Bulletin  Geol.  Surv.  491. 

t  Lindgren,  "Mineral  Deposits,"  288. 


424  MINERALOGY. 

Near  Laramie,  Wyoming,  are  "  lake  deposits  20-30  feet  deep, 
principally  of  sodium  sulphate,  mirabilite,  Na2SO4  +  ioH2O." 
The  upper  few  inches  is  nearly  pure  white  below  the  crystals  and 
intermixed  mud  containing  36  per  cent.  Na2SO4  (pure  mirabilite 
containing  44  per  cent.). 

The  same  mineral  separates  from  the  Great  Salt  Lake,  when  the 
temperature  is  low,  and  is  heaped  up  by  the  waves  on  the  beaches 
where,  if  not  collected,  it  redissolves  as  soon  as  the  temperature 
rises,  and  a  similar  winter  formation  takes  place  at  Lacu  Sarat, 
Roumania. 

Soda  Nitre. 

Soda  nitre  forms  in  small  amounts  as  the  result  of  the  action  of 
bacteria  on  organic  matter  and  the  union  of  the  nitric  acid  with  soda, 
and  may  accumulate  in  caves  as  at  Holmdale,  Idaho.  Somewhat 
larger  deposits  of  less  certain  origin  occur  in  Death  Valley,  Cali- 
fornia, along  the  shore  line  of  an  ancient  sea.* 

The  world's  great  deposits  are  in  Tarapaca  and  Antofagasta, 
Chili,  a  rainless,  desolate  region  3,000  feet  above  the  sea  between 
the  Andes  and  the  Coast  Ranges  and  near  the  latter.  Often  the 
deposits  are  only  ten  miles  from  the  sea. 

The  area  is  broken  by  transverse  ranges  into  a  series  of  plateaus 
or  "pampas"  which  slope  from  the  Andes  to  the  coast  ranges, 
Superficial  beds  of  common  salt  and  soda  nitre  I  to  6  ft.  thick 
occur  under  a  few  feet  of  earth,  the  nitrate  often  on  somewhat 
higher  ground,  but  at  other  times  they  are  mixed  indiscriminately, 
the  soda  nitre  averaging  about  25  per  cent. 

The  impure  soda  nitre  or  "caliche"  is  hand-picked  from  the 
associated  chlorides  and  sulphates  and  refined. 

The  origin  is  not  certain.!  The  soil  of  Venezuela  and  other 
parts  of  South  America  is  unusually  rich  in  nitrates.  Mountain 
floods,  which  occur  at  intervals  of  seven  or  eight  years,  may  have 
carried  the  soluble  nitrate  to  the  pampas  where  it  is  again  de- 
posited. Other  theories  are  the  leaching  of  bird  guano  and  the 
mingling  with  the  salt  waters  of  an  enclosed  basin. 

*  Mineral  Industry,  1914,  p.  673. 

t  Discussion,  Clarke,  Bulletin  U.  S.  Geol.  Survey,  491,  pp.  242-246. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.       425 

The  Carbonates  of  Sodium. 

The  carbonates  of  sodium  occur  in  soils  and  in  certain  lakes 
and  "playa"  lakes  (dry  in  summer,  flooded  in  the  wet  season). 
The  white  efflorescence  on  the  "playas"  is  a  mixture  of  these  with 
chlorides.  Trona  is  much  more  common  than  the  laboratory 
product,  natron. 

The  manner  of  their  deposition  from  weathering  solutions  is 
variously  attributed  to : 

1.  Direct  deposition  of  the  teachings  of  rocks*  poor  in  lime 
and  rich  in  soda  as  in  the  Lahontan  Lakes  of  Nevada,  in  which 
the  decomposing  rocks  are  rhyolites  and  andesites,  or  Owen's  Lake, 
California,  where  the  waters  run  through  volcanic  ash. 

2.  Reduction  from  alkaline  sulphates  by  algaef  as  in  part  at 
least  explaining  the  natron  lakes  of  Egypt. 

3.  Double  decomposition  between  sodium  sulphate  or  chloride 
and  calcium  bicarbonate  as  explaining  some  Hungarian  deposits. 

Examples  of  deposits,  some  of  which  have  been  worked  are: 

Searles  Lake,  California.^. — Contains  trona  in  "fish  bone"  crys- 
tals which  look  like  flat  splinters  of  wood  projecting  into  the 
ground  like  roots  for  6-7  inches. 

Green  River,  Wyoming,  where  borings  in  sandstone  yielded  at 
700  feet  an  almost  concentrated  solution  of  carbonates. 

Ragtown,  Nevada,  where  analyses  showed  an  average  Na2COs  47, 
NaHCO3  31,  H2O  16  per  cent. 

Owen's  Lake,  California. — The  dissolved  salts  being  one  third 
carbonates  of  soda. 

HALITE.— Rock  Salt,  Common  Salt. 

COMPOSITION. — NaCl,  (Na  60.6  per  cent.),  usually  impure. 

GENERAL  DESCRIPTION. — Halite  occurs  frequently  granular, 
sometimes  coarse,  often  dense  and  mixed  with  clay.  Colors 
white,  gray,  brown  or  blue  and  red  from  uncertain  coloring 
material,  green  from  copper,  brown  from  bituminous  substances. 
In  dry  countries  it  occurs  as  a  fibrous  efflorescence.  It  is  liable 
to  absorb  moisture  and  becomes  damp,  especially  when  containing 
calcium  or  magnesium  chlorides.  It  is  known  by  its  taste. 

*  Bulletin,  U.  S.  Geol.  Survey,  149,  229. 
t  Ibid.,  230. 
'   $  Mineral  Industry,  1914,  p.  676. 


426 


MINERALOGY. 


CRYSTALLIZATION. — Isometric  in  cubes  and  cavernous  crystals 
and  cubic  cleavages  often  with  symmetrical  etchings,  more  rarely 
other  forms. 


FIG.  414. 


FIG.  415. 


FIG.  417. 


Physical  Characters.     H.,  2.5.     Sp.  gr.,  2.4  to  2.6. 

LUSTRE,  vitreous.  TRANSLUCENT  to  transparent 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  colorless,  yellow,  brown,  deep  blue. 
TASTE,  salt.  CLEAVAGE,  cubic. 

BEFORE  BLOWPIPE,  ETC. — Decrepitates  violently,  fuses  very 
easily  and  colors  the  flame  yellow  and  may  be  volatilized.  Easily 
soluble  in  cold  water.  , 

SIMILAR  SPECIES. — The  taste  distinguishes  it  from  all  other 
minerals. 

REMARKS. — The  mode  of  occurrence,  type  localities  and  uses  have  been  described 
on  pp.  422-423. 

MIRABILITE.  —  Glauber  Salt. 

COMPOSITION.  —  Na2SO4  +  ioH2O  (Na2O  19.3,  SO3  24.8,  H2O 
55.9  per  cent.). 

GENERAL  DESCRIPTION.  —  Translucent)  white,  fibrous  crusts  or 
monoclinic  crystals,  closely  resembling  those  of  pyroxene  in  form 
and  angle.  On  exposure  loses  water  and  falls  to  powder. 

Physical  Characters.     H.,  1.5  to  2.     Sp.  gr.,  1.48. 

LUSTRE,  vitreous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TASTE,  salty  and  bitter. 

COLOR,  white  or  faintly  greenish. 

BEFORE  BLOWPIPE,  ETC.  —  On  charcoal  fuses,  colors  the  flame 
yellow  and  leaves  a  mass  which  will  stain  bright  silver.  In  closed 
tube  yields  much  water.  Easily  soluble  in  water. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        427 

REMARKS. — Type  occurrences  have  been  described  on  p.  423.  Others  are 
the  bottom  of  the  Bay  of  Kara  Bougas,  an  inlet  of  the  Caspian  Sea,  in  deposits 
sometimes  a  foot  in  thickness.  Massive  at  Logrdno,  Spain;  without  salt  in  great 
layers  at  Bompensieri,  Sicily;  Tiflis,  Tarapaca,  Chile;  New  Albany,  Ind.  In  gypsum 
in  Westmoreland  and  as  a  sublimation  product  at  Vesuvius. 

THENARDITE. — Na2SO4.  Twinned  tabular  orthorhombic  crystals  and  as  an 
efflorescence.  Soluble  in  water.  Found  at  Borax  Lake,  Cal.,  and  Villa  Rubia. 
Spain,  in  good  crystals,  dense  material  at  Stassfurt,  Prussia,  Rio  Verde,  Arizona,  etc, 

GLAUBERITE. — Na2SO4.CaSO4.  Tabular  monoclinic  crystals  and  lamellar 
masses  in  rock  salt  and  in  the  mud  of  borax  lakes. 

SODA  NITRE.— Chili  Saltpetre. 

COMPOSITION.— NaNO3,    (Na2O  36.5,  N2O5  63.5  per  cent). 

GENERAL  DESCRIPTION. — Rather  sectile  granular  masses  or  crusts 
of  white  color,  occurring  in  enormous  beds  and  as  an  efflorescence. 
Rarely  found  as  rhombohedral  crystals  of  the  forms  of  calcite.  On 
exposure  crumbles  to  powder. 

Physical  Characters.     H.,  1.5  to  2.     Sp.  gr.,  2.24  to  2.29. 
LUSTRE,  vitreous.  TRANSPARENT. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  colorless,  white  or  yellowish.    TASTE,  cooling  and  salty. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  deflagrates  less  violently 
than  nitre  and  becomes  liquid.  Colors  the  flame  yellow.  Very 
easily  soluble  in  water. 

REMARKS. — The  occurrence  and  uses  have  been  described  on  pp.  422,  424. 

TRONA.— Urao. 

COMPOSITION.— Na2CCyNaHCO3  -f  2H2O,   (Na2O  41.2,  CO2  38.9,  H2O  19.9.). 

GENERAL  DESCRIPTION. — Beds  and  thin  crusts  of  white  glistening  material,  often 
fibrous  and  occasionally  in  monoclinic  crystals.  It  is  not  altered  in  dry  air. 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  vitreous,  glistening.  Color,  white, 
gray,  yellowish.  Streak,  white.  H  ,  2.5  to  3.  Sp.  gr.,  2.11  to  2.14.  Taste,  alkaline. 

BEFORE  BLOWPIPE,  ETC. — Fuses-  easily,  coloring  flame  yellow.  In  closed  tube 
yields  water  and  carbon  dioxide.  Easily  soluble  in  water.  Effervesces  vigr/ously 
in  cold  dilute  acids. 

REMARKS. — The  chief  occurrences  have  been  described  on  p.  425;  others  are 
Armenia,  Venezuela  and  British  East  Africa. 

GAY-LUSSITE. — Na2CO3.CaCO3.5H2O.  White  monoclinic  pyramidal  crystals 
at  Soda  Lake,  Nevada;  Venezuela,  etc. 

THE    LITHIUM   MINERALS. 

The  minerals  described  are  : 


428  MINERAL  OG  Y. 


Phosphate 
Silicates 

Amblygonite 
Spodumene 
Lepidolite 
Petalite 

LiAl(SiO3)2, 
R3Al(SiO,)3 
LiAl(Si206)2 

Triclinic 
Monoclinic 
Monoclinic 
Monoclinic 

Lithia  is  also  a  constituent  of  a  series  of  double  phosphates 
such  as  triphyllite  and  triplite,  of  less  well-known  silicates  cookeite, 
eucryptite  and  of  certain  varieties  of  tourmaline. 

ECONOMIC   IMPORTANCE. 

About  3,000  tons  of  the  phosphate  amblygonite  were  pro- 
duced* in  the  Black  Hills  deposits  near  Keystone  and  shipped  to 
Newark  for  treatment.  The  silicates  are  little  if  at  all  used. 

The  chief  use  now  is  as  lithia  hydrate  in  prolonging  the  life  of  a 
storage  battery.  There  are  small  uses  in  photography,  medicine 
and  fireworks.  The  carbonate  was  formerly  extensively  used  as  a 
remedy  for  rheumatism. 

FORMATION   AND    OCCURRENCE    OF   LITHIUM    MINERALS. 

Lithia  is  present  in  most  igneous  rocks  but  chiefly  in  pegmatites 
of  soda-rich  rocks. 

Examples  are: 

Keystone,  South  Dakota. — Spodumene  and  amblygonite,  the  former  in  enormous 
crystals,  the  latter  in  nodules  up  to  1,000  Ibs.  in  weight. 

Montebras,  France:  Amblygonite.  Pa/a,  California:  Amblygonite,  lepidolite. 
Branchville,  Conn:  Amblygonite,  triphyllite,  spodumene.  Chesterfield,  Mass.: 
Spodumene.  Paris  and  Hebron,  Maine:  Amblygonite,  lepidolite. 


AMBLYGONITE. 

COMPOSITION. —Li  (A1.F)PO4,  (Li2O  10.1  percent,  generally  partly  replaced). 

GENERAL  DESCRIPTION.  —  A  cleavable  compact  massive  or  columnar  mineral  some- 
what resembling  orthoclase.  Sometimes  in  large  "indistinct  crystals. 

PHYSICAL  CHARACTERS.  —  H  =  6,  Sp.  0^=3.01-3.09.  Lustre,  pearly  to 
vitreous.  Streak,  white.  Brittle.  Translucent.  Color,  usually  white,  sometimes 
with  green,  blue,  yellow  or  brown  tints. 

BEFORE  THE  BLOWPIPE,  ETC,  —  Gives  characteristic  red  lithia  flame,  fuses  with 
intumescence  to  an  opaque  white  globule.  Soluble  in  sulphuric  acid  when  powdered. 

REMARKS.  —  Occurs  in  quantity  at  Pala,  California. 

USES.  —  Is  an  important  source  of  lithium  and  carries  a  comparatively  high  percentage 
of  this  element. 

*  Mineral  Industry,  1914,  p.  500. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        429 

SPODUMENE. 

COMPOSITION. —  LiAl(SiO3)2,  Li2O  8.4  per  cent,  with  some  sodium 
replacing  lithium. 

GENERAL  DESCRIPTION.  —  White  or  greenish- 
white  monoclinic  crystals,  sometimes  of  enormous 
size,  more  rarely  small  emerald-green,  and  larger 
lilac  colored  crystals.  Also  in  masses.  Character- 
ized by  an  easy  parting  parallel  a  in  addition  to 
the  prismatic  cleavage. 

CRYSTALLIZATION.  —  Monoclinic.  Axes  a  :  1)  \ 
c=  1.124  :  I  :  0.636;  /9  =  69°  4<y  Common, 
forms  :  the  pinacoids  a  and  b,  the  unit  prism,  my 
unit  pyramid  p,  the  pyramid  v  =  (a  :  b  :  2c)\  {221}  and  the 
clinodome  e  =  (oo  a  :  b  :  2c) ;  (021 }.  Supplement  angles  :  mm  = 
93°;  pp  =  63°  31';  vv  =  88°  34' ;  ee  =  107°  24'.  Optically  -f . 
Axial  plane  b. 

Physical  Characters.     H.,  6.5  to  7.     Sp.  gr.,  3.13  to  3.20. 
LUSTRE,  vitreous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  pale-green,  emerald,  green,  pink,  purple. 

BEFORE  BLOWPIPE,  ETC. — Becomes  opaque,  intumesces,  swells 
and  fuses  to  a  white  or  colorless  glass,  coloring  the  flame  purple- 
red,  especially  with  hydrochloric  acid.  Insoluble  in  acids. 

SIMILAR  SPECIES. — Distinguished  by  its  tendency  to  split  into 
thin  pearly  plates  and  by  the  red  flame. 

ALTERATIONS.  —  Spodumene  alters  to  /9  spodumene  by  replace- 
ment of  half  of  Li2O  by  Na2O  and  by  further  alteration  forms  cyma- 
tolite,  a  mixture  of  albite  and  muscovite. 

REMARKS. — Prominent  localities  are  mentioned,  p.  428.  The  gem  varieties  de- 
scribed later  occur  at  Alexander  Co.,  N.  C.  (hiddenite),  Pala,  Calif,  (kunzile),  Minas 
Geraes,  Brazil,  and  Madagascar  (spodumene). 

LEPIDOLITE.—  Lithia  Mica. 

COMPOSITION.  —  R3Al(SiO3)s.     R  —  Li,  K,  NaF,  etc.     Li2O,  4  to  6  per  cent. 

GENERAL  DESCRIPTION.  —  Scaly,  granular  masses  of  pale-pink  color  and  gray  trans- 
parent crystals,  with  easy  cleavage  into  elastic  plates. 

PHYSICAL  CHARACTERS.  —  Translucent.  Lustre,  pearly.  Color,  rose,  violet, 
lilac,  gray,  white.  Streak,  white.  H.,  2.5  to  4.  Sp.  gr.,  2.8  to  2.9.  Sectile 
Cleavage,  basal. 


430  MINERAL  OGY. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  to  a  white  glass.  Colors  the  flame  purple- 
red.  Partially  soluble  in  hydrochloric  acid. 

REMARKS.  — Found  in  considerable  quantity  near  Pala,  San  Diego  Co.,  California, 
with  red  tourmaline,  also  at  Paris  and  Hebron,  Me.,  Chesterfield,  Mass.,  Rozena, 
Moravia,  Uto,  Sweden,  and  elsewhere. 

USES.  —  It  is  a  source  of  lithium  salts. 

PETALITE. 

COMPOSITION.— Li  Al  (Si2O5)2. 

GENERAL  DESCRIPTION. — Glassy  white  or  gray  foliated  and  cleavable  masses  and 
rarely  minute,  colorless  crystals,  like  pyroxene  in  form. 

PHYSICAL  CHARACTERS. — Transparent  to  translucent.  Lustre,  vitreous.  Color, 
colorless^  white,  gray,  occasionally  pink.  Streak,  white.  H.,  6  to  6.5.  Sp.  gr.,  2.39 
to  2.46. 

BEFORE  BLOWPIPE,  ETC. — Phosphoresces  with  gentle  heat;  with  strong  heat, 
whitens  and  fuses  on  the  edges  and  colors  the  flame  carmine.  Insoluble  in  acids. 

REMARKS. — Found  at  Elba  in  tourmaline  granite  and  in  the  Iron  mines  of  Uto, 
Sweden.  In  this  country  at  Bolton,  Mass.,  and  Peru,  Maine. 

THE   AMMONIUM   MINERALS. 

The  minerals  described  are  : 

Chloride  Sal  Ammoniac  NH4C1  Isometric 

Sulphate  Mascagnite  (NH4)2SOi         Orthorhombic 

The  hypothetical  compound  radical  ammonium,  has  never  been 
separated  from  its  compounds.  Its  occurrence  in  nature  is  rare, 
and  its  minerals  while  of  great  theoretical  interest  do  not  occur  in 
commercial  quantities.  Its  compounds,  many  of  which  are  of 
great  importance  in  the  arts,  are  obtained  by  the  dry  distillation 
of  organic  matter,  and  notably  of  bituminous  coal  in  the  process 
of  gas  manufacture,  from  coke  ovens,  from  the  dry  distillation  of 
bones  and  from  the  gases  of  blast  furnaces  using  coal  as  fuel. 

SAL  AMMONIAC. 

COMPOSITION,— NH4C1,    (NH4  33.7,  Cl  66.3  per  cent.). 

PHYSICAL  CHARACTERS. — Transparent  to  translucent.  Lustre,  vitreous.  Color, 
colorless,  white,  yellowish.  Streak,  white.  H.,  1.5  to  2.  Sp.  gr.,  1.53.  Taste, 
pungent,  salt.  Cleavage,  parallel  to  octahedron. 

BEFORE  BLOWPIPE,  ETC.— Sublimes,  without  fusion,  as  white  fumes.  With  soda 
or  quicklime,  gives  odor  of  ammonia.  Easily  soluble  in  water. 

REMARKS. — Occurs  near  volcanoes,  burning  coal-beds  and  in  guano  deposits. 
Artificially,  it  is  a  by-product  from  gas-works. 

MASCAGNITE. 

COMPOSITION.— (NH4)2SO4,    ((NH4)2O  39.4,  SO3  60  6  per  cent.). 
GENERAL   DESCRIPTION. — Yellowish,  mealy  incrustations  on   lava  or   in  guano. 
Rarely  in  Orthorhombic  crystals. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        431 

PHYSICAL  CHARACTERS. — Translucent.  Lustre,  dull  or  vitreous.  Color,  lemon- 
yellow,  yellowish  or  gray.  Streak,  white.  H.,  2  to  2.5.  Sp.  gr.,  1.76  to  1.77.  Taste, 
pungent  and  bitter. 

BEFORE  BLOWPIPE,  ETC. — Sublimes  without  fusion.  With  soda  or  quicklime,  yields 
odor  of  ammonia.  Easily  soluble  in  water. 

REMARKS. — Occurs  on  lava  or  guano  or  near  burning  coal-beds.  It  is  artificially 
made  from  the  ammoniacal  liquors  of  gas-works,  coke-ovens,  and  blast  furnaces  and 
to  a  less  extent  is  a  by  product  from  the  manufacture  of  boric  acid  in  Tuscany. 

THE   BARIUM   MINERALS. 

The  minerals  described  are: 

Sulphate  Barite  BaSO4  Orthorhombic 

Carbonates  Witherite  BaCOs  Orthorhcmbic 

Barytocalcite       BaCa(CO3)2  Monoclinic 

Barium  occurs  in  a  few  silicates,*  hyalophane,  harmotome, 
also  in  the  phosphate  uranocircite,  the  nitrate,  nitrobarite  and  the 
carbonates  alstonite  and  bary*tocelestite. 

ECONOMIC   IMPORTANCE. 

The  production  of  barite  in  this  country  in  1915  was  108,547 
short  tons,  valued  at  $381,032,  chiefly  from  Missouri,  Georgia 
and  Tennessee.  England  and  Germany  usually  are  very  large 
producers. 

In  1914  there  was  importedf  into  this  country  about  50,000 
tons  of  barium  salts,  chiefly  baryta,  BaO,  but  also  blanc  fixe, 
lithophone,  and  the  carbonate,  binoxide  and  chloride. 

Barite  and  witherite  are  employed  chiefly  in  the  manufacture 
of  barium  sulphide,  chloride  and  oxide. 

Barium  sulphide  by  heating  barite  with  coal  slack  or  pitch,  barium  chloride  by 
dissolving  witherite  in  hydrochloric  acid  and  barium  oxide  by  roasting  witherite. 
From  these  the  other  salts  are  made. 

The  more  important  uses  are{  as  pigments  in  the  ground  state 
or  as  the  artificial  compounds  blanc  fixe  and  lithophone;  and  as 
the  peroxide  used  in  making  hydrogen  peroxide.  Minor  uses 
are  in  the  making  of  white  rubber,  artificial  ivory,  boiler  com- 
pounds, and  special  glasses  and  in  preventing  efflorescence  on 
bricks.  There  is  a  reported§  use  by  Germany  in  the  manufacture 

*  Also  celsian,  barylite,  brewsterite,  edingtonite,  barytbiotite. 

f  Mineral  Industry,  1914,  p.  65. 

{  Mineral  Resources  U.  S.,  1914,  p.  63. 

§  Mineral  Industry,  1914,  p.  71. 


432  MINERAL  OGY. 

of  sulphuric  acid  by  oxidizing  the  H^S  released  on  treatment  of 
the  sulphide  by  hydrochloric  acid. 

FORMATION  AND    OCCURRENCE    OF   BARIUM  DEPOSITS. 

Barium  is  present  in  the  earth's  crust  to  the  extent  of  about 
one  tenth  of  one  per  cent.,  probably  as  silicate  and  the  leucite 
and  analcite  rocks  of  Montana  and  Wyoming  contain  as  much 
as  one  per  cent. 

The  economic  deposits  are  sulphate  or  carbonate  and  occur  as: 

Veins  Associated  with  Metallic  Ores. 

Barite  is  one  of  the  most  common  gangue  minerals.  It  is 
separated*  by  hand  picking  in  large  quantities  from  the  lead  and 
zinc  veins  of  Durham,  Northumberland,  Cumberland  and  West- 
moreland, England ;  and  vein  barite  is  mined  at  Larn,  Ireland.  The 
only*  economic  deposit  of  witherite  ;s  at  Fourstones,  Northumber- 
land. Norway  also  produces  barite  as  a  by  product  in  lead  mining 
and  in  this  country  it  is  abundant  in  veins  and  cavities  with  galena 
and  sphalerite  in  Jefferson  and  Franklin  Counties,  Missouri. 

Veins  Free  from  Metallic  Ores  or  as  Replacements. 

Many  such  deposits  occur  in  Virginia  in  limestone  as  a  series 
of  lenses  and  fractures  sometimes  connected.  It  is  mined  in 
open  cuts  in  Washington  Co.,  Mo.  Occurs  in  veins  in  sandstones 
of  Hesse. 

Residual  Deposits. 

Imbedded  in  clay  as  a  result  of  the  weathering  of  a  limestone  or 
other  rock.  Such  deposits  occur  in  Missouri,  Virginia,  and 
Cartersville,  Georgia.  The  compact  Bologna  spar  occurs  in  marl 
near  Bologna. 

BARITE.— Heavy  Spar. 

COMPOSITION. — BaSO4,  (BaO  65.7,  SO3  34.3  per  cent.),  some- 
times with  some  strontia,  silica,  clay,  etc. 

GENERAL  DESCRIPTION. — A  heavy  white  or  light-colored  min- 
eral, vitreous  in  lustre.  It  occurs  in  orthorhombic  crystals,  which 
are  frequently  united  by  their  broader  sides  in  crested  divergent 
groups,  and  varying  insensibly  from  this  to  masses  made  up  of 
curved  or  straight  lamellae  and  cleavable  into  rhombic  plates.  It 
occurs  also  granular,  fibrous,  earthy,  stalactitic  and  nodular. 

*  Mineral  Industry,  1914,  p.  71. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        433 
FIG.  419.  FIG.  420.  FIG.  421. 


FIG.  422. 


FIG.  423. 


FIG.  424. 


CRYSTALLIZATION. — Orthorhombic.  Axes  a  :  b  :  c  =  0.815  :  i  : 
1.314. 

Unit  prism  m,  base  c  and  domes  d  =  (QO  &  :  b  :  c);  {on }  and 
n  =  (a  :  oo  b  :  \c}\  {102}  are  the  most  common  forms.  Supple- 
ment angles  are  mm  =  78°  23';  cd  =  52°  43';  en  =  38°  52'. 

Optically  +.  The  axial  plane  parallel  b  and  the  acute  bisectrix 
normal  to  a.  Axial  angle  with  yellow  light  2E  =  63°  12'. 

Physical  Characters.     H.,  2.5  to  3.5.     Sp.gr.,  4.3  to  4.6. 
LUSTRE,  vitreous  and  pearly.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white  or  light  shades  of  yellow,  brown,  red  or  blue. 

CLEAVAGE,  basal  and  prismatic  (101°  37'  being  prism  angle). 

BEFORE  BLOWPIPE,  ETC. — In  forceps,  decrepitates  and  fuses, 
coloring  the  flame  yellowish-green  and  leaving  an  alkaline  residue. 
With  soda,  on  charcoal,  gives  sulphur  reaction.  Insoluble  in  acids. 

SIMILAR  SPECIES. — Distinguished-  among  non-metallic  minerals 
by  its  high  specific  gravity,  insolubility  and  green  flame. 

REMARKS. — Type  occurrences  and  uses  are  described  on  p.  432.  Celebrated 
crystal  localities  are  Derbyshire,  England;  Felsobanya,  Hungary;  Clausthal,  Harz; 
Pribram,  Bohemia;  Bad  Lands,  Dakota;  Sterling,  Colorado;  Cheshire,  Connecticut. 

WITHERITE. 

COMPOSITION. — BaCO3  (BaO  77.7,  CO2  22.3  per  cent.). 

GENERAL    DESCRIPTION. — Heavy   white   or   gray    translucent 
masses  of  vitreous  lustre,  sometimes  with  small  indistinct  crystals 
or  globular  or  botryoidal  groups.     Also  granular,  columnar  and 
in  crystals  resembling  those  of  quartz. 
29 


434 


MINERALOGY, 


CRYSTALLIZATION. — Orthorhombic.  Axes  a  :  b  :  c  =  0.603  :  J  : 
0.730.  Crystals  always  repeated  twins  resem- 
bling hexagonal  pyramids  with  usually  horizon- 
tal striations  or  deep  grooves  on  the  faces,  Fig. 
428.  Optically  — . 

Physical  Chaeacters.     H.,  3  to  4.     Sp.  gr.  ,4.29 

to  4-35- 

LUSTRE,  vitreous.  TRANSLUCEFT. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  gray,  yellowish. 

Cumberland,  Eng.         BEFORE  BLOWPIPE,  ETC. — Fuses  rather  easily, 
coloring  flame  yellowish-green  and  becoming  al- 
kaline.    Soluble  in  dilute  hydrochloric  acid,  with  effervescence, 
and  less  rapidly  soluble  in  strong  acid. 

SIMILAR  SPECIES.  —  Distinguished  by  its  weight,  effervescence 
with  acids  and  green  flame. 

REMARKS. — Occurs  in  veins  with  lead  ores  at  Fallowfield,  Northumberland,  and 
Alston,  Cumberland,  and  in  small  amounts  near  Lexington,  Ky.,  and  on  the  north 
shore  of  Lake  Superior.  The  most  productive  mines  are  at  Fallowfield  in  England. 

BARYTOCALCITE. — BaCa(CO3)2.  Monoclinic  needles  and  masses  of  yellowish- 
white  color  found  in  the  witherite  locality.  Always  yields  a  weak  manganese  test. 

THE    STRONTIUM   MINERALS. 

The  minerals  described  are  : 

Carbonate  Strontianite  SrCOs  Orthorhombic 

Sulphate  Celestite  SrSO4  Orthorhombic 

Strontium  constitutes  about  nine  per  cent,  of  the  silicate 
brewsterite  and  is  found  in  small  amounts  in  aragonite,  calcite, 
dolomite  and  barite. 

ECONOMIC   IMPOTRANCE. 

In  this  country  it  is  unimportant;  none  was  produced*  in  1914 
and  the  imported  material  was  valued  at  $1,016.  Germany  prior 
to  the  war  used  100,000  tons  of  hydroxide  per  year  in  the  beet 
sugar  industry,  there  is  a  small  use  of  iodide,  bromide  and  lac- 
tate  in  medicine  and  the  nitrate  is  the  basis  of  the  red  fire  used  in 
fireworks  and  in  night  signals  by  boats  or  trains. 

*  Mineral  Resources  U.  S.,  1914,  p.  15. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        435 

Strontium  hydroxide  is  made  by  converting  the  sulphate  into  sulphide,  bringing 
this  sulphide  into  solution  in  water,  and  precipitating  the  strontium  hydroxide  by 
means  of  sodium  hydroxide.  It  is  used  to  precipitate  sugar  from  molasses  as  a 
strontium  compound  from  which  crystalline  sugar  can  later  be  obtained. 

FORMATION  AND   OCCURRENCE   OF   STRONTIUM    MINERALS. 
Strontium  is  estimated  to  constitute  four  one-hundredths  of 
one  per  cent,  of  the  earth's  crust  and  the  state  in  which  it  is  com- 
bined is  not  known.     The  sulphate  and  carbonate  occur: 

In  Veins. 

The  great  Westphalian  deposits  of  strontianite  consist  of  large 
masses  in  veins  in  chalk  and  marl. 

Occurrences  in  ore  veins  are  Clausthal,  Harz;  Braunsdorf,  Saxony;  Strontian, 
Scotland;  Condorcet,  France. 

In  Chemical  Sediments. 

The  Sicilian  deposits  of  sulphur  due  to  altered  gypsum  are  rich 
in  celestite  and  are  an  economic  deposit.  Concentrations  in  lime- 
stone are  numerous  as  at  Strontian  Island,  Lake  Erie;  Monroe 
Co.,  Michigan;  Wallis,  Switzerland.  Concentrations  with  gypsum 
and  halite  occur  at  Ischl,  Austria;  Silver  Lake,  California  and 
Gila  Bend,  Arizona;  Bristol,  England. 

CELESTITE. 

COMPOSITION — SrSO4,    (SrO  56.4,  SO3  43.6  per  cent.). 

GENERAL  DESCRIPTION. — A  white  translucent  mineral,  often  with 
a  faint  bluish  tinge.  Occurs  in  tabular  to  prismatic  orthorhombic 
crystals,  fibrous  and  cleavable  masses,  and  rarely  granular.  It  is 
notably  heavy,  and  has  a  general  resemblance  to  barite. 

CRYSTALLIZATION.  —  Orthorhombic.  Axes  a  :  ~&  :  c  =  0.779  :  r 
:  1.280. 

The  common  forms  are  the  base  c,  the  unit  prism  m  and  the 
domes  n  and  d.  The  supplement  angles  are  mm  =75°  50' ;  en  = 
39°  25';  «/=52°. 

FIG.  426.  FIG.  427. 


Sicily.  Lake  Erie. 


MINERAL  OGY. 


Optically  +.  Axial  plane  b.  Acute  bisectrix  normal  to  a. 
Axial  angle  with  yellow  light  2E=  88°  38'. 

Physical  Characters.     H.,  3  to  3.5.     Sp.  gr.,  3.95  to  3.97. 

LUSTRE,  vitreous  or  pearly.         TRANSPARENT,  nearly  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white  colorless,  pale  blue  or  reddish. 

CLEAVAGE.—  Basal  and  prismatic,  yielding  rhombic  plates  in 
which  the  rhomb  angles  are  104°  10'  and  75°  50'. 

BEFORE  BLOWPIPE,  ETC.—  Fuses  easily  to  a  white  pearly  glass 
and  colors  the  flame  crimson.  Usually  decrepitates  and  becomes 
alkaline.  With  soda  on  charcoal  gives  sulphur  reaction.  In- 
soluble in  acids. 

SIMILAR  SPECIES.  —  Distinguished  from  barite  by  its  red  flame 
and  from  other  minerals  by  its  high  specific  gravity,  insolubility 
and  red  flame. 

REMARKS.  —  Occurs  as  described  on  p.  435. 


STRONTIANITE. 

COMPOSITION. — SrCO3,    (SrO  70.1,  CO2  29.9  per  cent.). 

GENERAL  DESCRIPTION. — Usually  found  as  yellowish- white  or 
greenish-white  masses  made  of  radiating  imperfect  needle  crystals 
and  spear-shaped  crystals,  very  like  those  of  aragonite.  Also 
fibrous  or  granular  and  only  rarely  in  distinct  orthorhombic  crys- 
tals, sometimes  of  considerable  size. 

Physical  Characters.     H.,  3  to  3.5      Sp.  gr.,  3.68  to  3.72. 

LUSTRE,  vitreous.  TRANSLUCENT. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  pale  yellowish  or  greenish-white,  also  green,  gray  and 
colorless. 

BEFORE  BLOWPIPE,  ETC. — In  forceps  swells,  sprouts,  colors  the 
flame  crimson,  fuses  on  the  edges  and  becoming  alkaline.  Soluble 
in  cold  dilute  acids  with  effervescence. 

SIMILAR  SPECIES. — Differs  from  calcite  and  aragonite  in  fusibility, 
higher  specific  gravity  and  purer  red  flame.  The  flame  and  effer- 
vescence distinguish  it  from  all  other  minerals. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        437 

REMARKS. — Strontianite  is  found  in  the  United  States  chiefly  in  the  State  of  Ne\v 
York,  especially  at  Schoharie,  Muscalonge  Lake,  Chaumont  Bay,  Theresa  and  Clinton. 
Strontianite  used  in  the  German  beet  sugar  industry  is  largely  obtained  from  West- 
phalia. 

THE   CALCIUM    MINERALS. 

THE  minerals  described  are  : 

Fluoride 
Sulphates 

Carbonates 


Fluorite 

CaF2 

Isometric 

Anhydrite 

CaSO< 

Orthorhombic 

Gypsum 

CaSCX  4-  2H,O 

Monoclinic 

Aragonite 

CaCO, 

Orthorhombic 

Calcite 

CaCO3 

Hexagonal 

Dolomite 

CaCO3.MgCO8 

Hexagonal 

Ankerite 

(Ca.Mg.Fe)  CO, 

Hexagonal 

Among  the  calcium  silicates  considered  are  anorthite,  labra- 
dorite,  oligoclase,  pyroxene,  wollastonite,  amphibole,  garnet,  vesu- 
vianite,  datolite,  epidote,  prehnite,  and  the  zeolites;  other  non 
silicates  are  apatite,  scheelite,  autunite. 

ECONOMIC   IMPORTANCE. 

Aside  from  apatite  and  scheelite  the  economically  important 
minerals  are  the  carbonates,  sulphates  and  fluoride. 

Calcite. 

Massive  CALCITE  and  DOLOMITE,  that  is  limestone  and  marble, 
are  quarried  in  enormous  quantities,  the  production  of  limestone 
exceeding  in  value  even  that  of  granite. 

In  1914  there  was  produced  in  this  country:* 

Estimated  Weight,  Tons.  Value. 

Marble 400,000  $  8,121,412 

Limestone  burned  as  lime ...     3,380,963  13,247,676 

Other  limestone 65,000,000  38.745.429 

68,780,963  $60,114,517 

In  addition  to  the  uses  enumerated  above,  limestone  is  used  for 
hydraulic  cements  and  in  1914  about  15,000,000  tons  of  Portland 
and  other  cements  were  produced  in  the  United  States,  valued  at 
$80,533,203. 

The  great  producers  were  in  order  of  production: 

Marble  Limestone  Lime  Cement 

Vermont  Pennsylvania  Pennsylvania  Pennsylvania 

Tennessee  Ohio  Ohio  Indiana 

Georgia  Indiana  Virginia  New  York 

Alabama  New  York  Wisconsin  Illinois 

*  From  Mineral  Resources  U.  S.,  1914,  pp.  363-373,  864-880  and  Mineral  Industry, 
1914,  p.  84. 


438  MINERALOGY. 

The  great  uses  are  in  order  of  importance. 

Marble,  interior  building,  monuments,  exterior  building. 

Limestone,  road  metal,  flux,  concrete,  road  ballast,  fertilizers. 

Lime,  building,  fertilizers  (slaked),  paper  mills,  tanneries,  chemical  work,  including 
the  soda  ash  process,  bleaching  powder,  calcium  carbide  and  glass  and  calcium 
cyanamide. 

Minor  uses  were:  Lithographic  limestone,  of  which  there  was  a  small  production 
in  Kentucky  and  Iowa.  Paris  white,  and  whiting  (ground  chalk)  used"  for  kal- 
somine,  putty  and  whitewash. 

Gypsum. 

The  commonest  of  all  sulphates.  The  world  uses*  over  five 
million  tons  annually  of  which  about  two  fifths  comes  from  the 
United  States,  two  fifths  from  France  and  half  of  the  rest  from 
Canada. 

A  comparatively  small  amount  of  fine-grained  material  is  used 
as  "alabaster"  in  statues,  vases,  columns,  etc.,  and  a  large  amount 
of  poor-grade  gypsum  is  ground  as  a  fertilizer  and  of  "  selenite  "  as  a 
constituent  of  wood  pulp. 

The  rest,  probably  three  fourths  of  all,  is  burned  to  produce 
varieties  of  quick  or  slow  setting  plaster  of  Paris,  the  use  of  which 
mixed  with  fibre  or  with  layers.of  paper  has  greatly  increased  in 
modern  buildings. 

Fluorite. 

There  is  an  increasing  production  and  use  of  fluorite  chiefly 
for  Use  as  a  flux  in  basic  open  hearth  steel. .  .  The  production  in 
1915  in  the  United  States  wasf  136,941  tons,  valued  at  $764,475. 
Nearly  all  came  from  Illinois  and  Kentucky  and  83  per  cent,  of  it 
was  sold  for  use  in  the  smelters. 

Other  uses  are  in  producing  opalescent  glass  and  enamels, 
hydrofluoric  acid  and  artificial  cryolite^  for  use  in  the  aluminum 
industry. 

FORMATION   AND    OCCURRENCE   OF   THE   CALCIUM    MINERALS. 

The  earth's  crust  is  estimated  to  contain  3.18  per  cent,  of 
calcium,  the  percentage  in  the  igneous  rocks  being  a  little  higher, 

*  Mineral  Industry,  1914,  p.  388;  1913,  U.  S.,  2,357,752;  France,  2,150,900; 
Canada,  577,442. 

f  Mineral  Resources  U.  S.,  1915,  p.  33. 
J  By  fusion  with  bauxite  and  soda  ash. 


MINERALS  IMPORTANT  IN   THE  INDUSTRIES.       439 

the  greater  portion  being  present  in  the  plagioclase  feldspars, 
the  monoclinic  pyroxenes,  and  the  amphiboles. 

The  calcium  minerals  here  considered  may  be  classed  as  follows: 

Separation  from  Magma  or  Volcanic  Exhalations. 

FLUORITE  is  an  accessory  in  granite,  gneiss,  quartz  porphyry, 
or  syenite  and  sometimes  in  volcanic  lavas  as  result  of  the  action 
of  fluorine-bearing  gases. 

ANHYDRITE  crystals  occur  in  cavities  of  lava  at  Santorin. 

GYPSUM  may  form  by  the  action  of  volcanic  gases  or  sulphurous 
waters  on  rocks  containing  calcium  as  in  the  Sicilian  sulphur 
deposit.* 

In  Veins  as  Gangue. 

FLUORITE,  f  is  next  to  quartz  and  the  carbonates,  the  most  com- 
mon gangue  mineral,  as  occurring  at  Cripple  Creek,  Colorado, 
with  gold  tellurides;  Kongsberg,  Norway,  with  silver;  Rosiclare, 
Illinois  and  Salem  and  Marion,  Kentucky,  with  galena  and  sphal- 
erite; north  of  England  with  lead;  Saxon  Voigtland  with  copper; 
and  also  as  the  most  constant  gangue  of  tin  veins. 

CALCITE,  which  next  to  quartz  is  the  great  gangue  mineral,  is 
comparatively  rare  in  the  old  gold  veins  but  occurs  in  the  "old" 
silver  veins,  as  at  Kongsberg,  Norway  and  Cobalt,  Ontario,  and 
abundantly  in  the  "young"  gold-silver  veins  and  the  galena 
sphalerite  and  pyrite  veins. 

DOLOMITE  is  often  with  calcite,  as  at  Schneeberg,  Saxony,  and 
Pribram,  Bohemia. 

In  Veins  Without  Metals. 

FLUORITE.  —  Some  of  the  veins  of  Illinois  and  Kentucky  are 
nearly  metal-free.  Similar  veins  exist  in  San  Roque,  Argentina; 
sometimes  they  widen  into  caverns  lined  with  fluorite,  as  at 
Macomb,  New  York,  in  which  one  cavern  yielded  fifteen  tons  of 
fluorite. 

CALCITE.  —  The  famous  Iceland  spar  quarries  of  Reydarfjorden 
are  veins  in  basalt,  the  most  desirable  material  occurring  in  a 
red-gray 


*  Weinschenck,  "Grundziige  der  Gesteinkunde,"  p.  240. 

t  Commercial    deposits,    Illinois,    Kentucky,    Weardale,    Durham,    Castleton, 
Derbyshire. 

|  Merrill's  "Metallic  Minerals,"  p.  136. 


440  MINERALOGY. 

Replacement  Deposits. 

FLUORITE  may  replace  limestone  as  at  the  Florence  mine, 
Montana,*  or  the  country  rock  near  a  tin  deposit. f 

DOLOMITE. — "  Dolomitization  "  in  metasomatic  lead  silver  zinc 
deposits  is  attributed^  to  "  metasomatic  action  of  solutions  con- 
taining CO2  and  the  MgCO3  upon  the  limestone." 

The  increase  in  percentage  of  magnesium  in  the  marine  marls 
of  Sweden,  and  in  coral  may  be  called  replacements. 

As  Chemical  Sediments. 

FLUORITE. — The  dense  fluorite  of  Stolberg,  Harz,  and  the 
Pyrenees  are  apparently  chemical  sediments. § 

ANHYDRITE  is  practically  always  a  chemical  sediment  formed  as 
such  or  formed  as  gypsum  and  changed  by  the  action  of  brine  || 
to  anhydrite. 

The  general  association  is  with  halite  and  gypsum.  Large 
deposits  exist  at  Zechstein,  Harz,  at  Cordova,  Spain;  Stassfurt, 
Germany  (300  feet  thick) ;  Hillsborough,  Nova  Scotia,  under  the 
gypsum,  Spur,  Texas;  Louisiana;  Southern  California. 

Beds  of  anhydrite  and  halite  at  the  surface  are  rare.  Usually 
the  halite  is  dissolved  and  the  anhydrite  is  changed  to  gypsum. 

GYPSUM  occurs  in  immense  deposits  as  a  chemical  sediment: 
(a)  Without  salt  beds  indicating  incomplete  evaporation  or  sub- 
sequent leaching  out  of  the  salt  as  in  the  "  Keupergrips "  of 
Wiirtemberg,**  or  the  "gypsite"  surface  deposits  with  clay  in 
Kansas,  Oklahoma  and  Texas,  and  the  "white  sands"  of  Otero, 
New  Mexico. 

Near  Fillmore.ft  Utah,  deposits  of  sand-like  gypsum  are  formed  by  the  winds 
blowing  from  the  dry  beds  of  playa  lakes  the  minute  crystals  deposited  by  evapora- 
tion. The  material  forms  dunes  estimated  to  contain  450,000  tons  of  gypsum. 

With  salt  beds  sometimes  as  an  original  deposit,  usually  under- 
lying the  salt  and  formed  before  the  solutions  were  saturated  with 

*  Lindgren,  "Mineral  Deposits,"  p.  164. 

t  Beyschlag,  Vogt  and  Krusch  (Truscott),  p.  415. 

J  Ibid.,  p.  718. 

§  Weinschenck  believes  them  to  be  secondary  concentrations.  "  Grundziige  der 
Gesteinkunde,"  p.  237. 

||  Van't  Hoff  established  that  gypsum  in  NaCl  solutions  changes  to  anhydrite  at 
about  25°  C.  to  30°  C.  Crystals  of  gypsum  sinking  through  brine  would  be  con- 
verted into  anhydrite.  Lindgren,  p.  269. 

c  "Grundziige  des  Gesteinskunde "  (Weinschenck),  p.  240. 

ft  Merrill's  "Non-Metallic  Minerals,"  p.  341. 


MINERALS  IMPORTANT  IN   THE  INDUSTRIES.        441 

salt,  or  at  temperatures  below  25°  C.     More  frequently  secondary 
to  anhydrite  and  overlying  it. 

Famous  deposits  exist  at  Hillsborough,  New  Brunswick;  Went- 
worth,  Nova  Scotia;  Michigan;  Northern  Ohio ;  Erie  and  Onondaga 
Counties,  New  York;  Fort  Dodge,  Iowa;  Louisiana;  Montmartre, 
France;  the  middle  and  north  of  England;  and  the  alabaster 
locality  of  Castellina,  Tuscany. 

Calcium  Carbonate. 

Chemical  sediments  of  calcium  carbonate  occur.  Springs  form 
"calc  sinter,"  rivers  deposit  "travertine"  as  at  the  waterfalls  of 
Tivoli,  thick  beds  of  cellular  material  form  known  as  "calc  tufa" 
as  at  Pyramid  and  Winnemucca  Lakes,  Nevada.*  Stalactites 
and  stalagmites  form  in  caves.  Flos  ferri  and  compact  onyx 
marbles,  all  are  chemical  sediments  and  when  bicarbonate  solu- 
tions enter  the  ocean  there  may  be  direct  precipitation,  as  in  the 
delta  of  the  Rhonef  and  along  the  coast  of  Florida. 

Sinter  and  travertine  and  other  chemical  sediments  may  be 
due  in  part  to  the  cooperation  of  organisms,  and  chalk  beds, 
fresh  water  marls,  coral  and  shell  limestones  are  formed  from 
their  shells  and  frameworks. 

DOLOMITE  may  be  a  true  sediment  as  at  Ulm,  Bavaria,  and  the 
deposit  from  the  mineral  spring  at  St.  Allyre,  France.  More 
frequently  it  is  an  alteration  or  replacement  of  calcium  carbonate. 

FLUORITE.  —  Fluor  Spar. 

COMPOSITION. — CaF2,    (Ca  5  i.i,  F  48.9  per  cent.). 

GENERAL  DESCRIPTION. — Usually  found  in  glassy  transparent 
cubes  or  cleavable  masses  of  some  decided  yellow,  green,  purple 
or  violet  color.  Less  frequently  granular  or  fibrous.  Massive 
varieties  are  often  banded  in  zigzag  strips  of  different  colors. 

CRYSTALLIZATION.  —  Isometric.  Usually  cubes  with  modifying 
forms,  especially  the  tetrahexahedron  e  =  (a  :  20,  :  oo  a),  {210}; 
the  dodecahedron  ^/and  the  hexoctahedron  t  =  (a  :  2a  :  40),  {421 }. 
The  cube  faces  are  often  striated  parallel  to  the  edges  or  with 
vicinal  faces,  p.  78,  giving  the  appearance  of  a  very  flat  tetra- 
hexahedron. Rarely  found  in  octahedrons,  sometimes  formed  by 

*  Bulletin  491  U.  S.  Geol.  Survey,  525. 

t  Ibid. 

J  Ibid.,  536. 


442 


MINERALOGY. 


the  grouping  of  small  cubes  in  parallel  positions.      Penetration 
twins  common. 

Index  of  refraction  for  yellow  light  1.4339. 

Physical  Characters.     H.,  4.     Sp.  gr.,  3.01  to  3.25. 

LUSTRE,  vitreous.  TRANSPARENT  to  nearly  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  wine-yellow,  green,  violet,  blue,  colorless,  brown,  black. 


FIG.  428. 


FIG.  429, 


FIG.  430. 


CLEAVAGE,  octahedral  at  angles  of  70°  31'. 

BEFORE  BLOWPIPE,  ETC. — In  closed  tube  at  a  low  heat  becomes 
phosphorescent.  In  forceps  fuses  to  a  white  opaque  glass  and 
colors  the  flame  red.  Soluble  in  hydrochloric  acid.  Heated  with 
acid  potassium  sulphate  or  sulphuric  acid,.fumes  are  set  free  which 
corrode  glass. 

SIMILAR  SPECIES. — Recognized  by  cleavage  and  crystals  and  by 
the  etching  test.  When  cut  it  may  resemble  aqua  marine,  yellow 
topaz,  etc.,  but  js  distinguished  by  softness. 

REMARKS. — Occurrences  and  uses  as  stated  on  pp.  438  and  439.  The  brighter 
colored  varieties  are  cut  into  vases,  figures  or  imitation  gems. 

ANHYDRITE. 

COMPOSITION.— CaSO4,    (CaO  41.2,  SO3  58.8  per  cent.). 

GENERAL  DESCRIPTION. — Granular,  marble-like  or  sugar-like 
in  texture,  or  as  fibrous  and  lamellar  masses  of  white,  gray,  bluish 
or  reddish  color.  Cleavage  in  three  directions  at  right  angles. 
Rarely  in  orthorhombic  crystals. 

Physical  Characters.     H.,  3  to  3.5.     Sp.  gr,  2.9  to  2.98. 
LUSTRE,  vitreous  or  pearly.  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  gray,  bluish,  brick-red.  CLEAVAGES  at  right  angles. 


MINERALS   IMPORTANT  IN   THE  INDUSTRIES.        443 


BEFORE  BLOWPIPE,  ETC. — Fuses  to  a  white  enamel  and  colors 
the  flame  red.  With  soda  yields  a  sulphur  reaction.  Soluble 
slowly  in  acids. 

SIMILAR  SPECIES. — Differs  from  gypsum  in  being  harder  and 
not  yielding  decided  test  for  water.  Does  not  effervesce  in  acids 
like  marble.  Cleavage  pseudo-cubic. 

Varieties. 

Anhydrite  of  direct  deposition,  usually  dense,  often  enclosing  a 
little  clay  or  pyrite,  halite,  crystals  of  dolomite,  boracite,  fluorite, 
quartz.  The  color  is  white,  red  from  iron,  blue  gray  from  clay, 
and  an  unexplained  azure  blue. 

Tripe  stone  (Gekroses  stein). — Thin,  closely  folded  layers  in  salt 
clay,  such  as  occur  in  Galicia. 

Vulpinite,  a  scaly  siliceous?  variety,  which  is  cut  and  polished. 

REMARKS. — Occurs  as  a  chemical  sediment,  as  described  on  p.  440,  in  mountain 
masses.  It  is  rare  in  ore  deposits.  The  best  crystals  are  found  embedded  in  the 
Stassfurt  kieserite;  others  occur  on  massive  anhydrite  at  Berchtesgaden,  Bavaria. 

GYPSUM.— Selenite,  Alabaster. 

COMPOSITION.— CaSO4  +  2  H2O,  (CaO  32.5,  H2O  20.9,  SO3 46.6 
per  cent). 

GENERAL  DESCRIPTION. — Soft  colorless  white  or  slightly  tinted 
masses,  which  may  be  granular  or  compact,  or  may  be  translucent 
and  silky,  fibrous  or  transparent  and  cleavable  into  plates  and  strips. 
Also  in  transparent  cleavable  monoclinic  crystals. 

FIG.  431.  FIG.  432.  FIG.  433.  FIG.  434. 


Utah. 


CRYSTALLIZATION.  —  Monoclinic.     /?  =  80°  42'.     Axes  a  :  b  :  J 

0.690  :  I  :  0.412. 

Frequently  the  negative  unit  pyramid  p,  with  the  unit  prism  m 


444  MINERALOG  Y. 

and  clino-pinacoid  b,  Fig.  432,  or  these  twinned,  Fig.  433,  or  with 
dome  r  =  (a  :  <x>  b  :  fc),  {103} ;  Figs.  431  and  434.  Supplement 
angles  mm  =  68°  30';  pp  =  36°  12';  cr  =  11°  29'. 

Physical  Characters.     H.,  1.5  to  2.     Sp.  gr.,  2.31  to  2.33. 

LUSTRE,  pearly,  silky,  vitreous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle,  laminae  flexible. 

COLOR,  white,  colorless,  gray,  red,  yellow,  brown. 

CLEAVAGE,  clino-pinacoid  perfect,  unit  ortho-dome  fibrous,  and 
ortho-pinacoid  conchoidal.  The  cleavage  fragments  are  rhombic 
plates  with  angles  66°  and  114°. 

BEFORE  BLOWPIPE,  ETC.  —  When  heated  quickly  becomes  white 
and  opaque  and  fuses  to  an  alkaline  globule,  coloring  the  flame 
yellowish-red.  In  closed  tube  yields  water.  Soluble  in  hydro- 
chloric  acid.  The  powdered  dehydrated  mineral  when  mixed  with 
water  will  form  a  compact  mass.  Gives  sulphur  reaction. 

VARIETIES. 

Selenite. — Crystals  or  transparent  cleavable  masses. 

Satin  Spar. — Fine  translucent  fibrous  varieties  with  sheen  of 
silk. 

Alabaster. — Compact  and  fine  grained,  suitable  for  carving. 

Rock  Gypsum. — Scaly,  granular  or  dull  colored  and  compact. 

Gypsite. — An  impure  unconsolidated  earthy  or  sandy  form  of 
gypsum,  which  in  many  places  is  found  to  contain  a  suitable 
percentage  of  foreign  material  so  that  the  addition  of  a  retarder 
is  not  necessary  to  effect  a  slow  set. 

SIMILAR  SPECIES. — Talc,  brucite,  mica,  calcite,  heulandite,  stil- 
bite.  It  is  softer  than  all  but  talc,  lacks  the  greasy  feeling  of  talc 
and  is  further  characterized  by  quiet  solubility,  cleavages  and 
calcium  flame. 

REMARKS. — The  commonest  of  sulphates  and  chiefly  a  chemical  sediment,  as 
described  on  p.  440,  and  not  usually  an  original  separate  but  derived  from  anhydrite, 
usually  in  dense  masses,  which  may  include  large  crystals. 

Famous  crystal  localities  are  Montmartre,  Paris;  Girgenti,  Sicily;  Wayne  Co., 
Utah;  Ellsworth  Co.,  Ohio.  In  Mammoth  Cave,  Kentucky,  it  imitates  rosettes, 
flowers,  etc. 

ARAGONITE.— Flos  Ferri. 

COMPOSITION.— CaCO3,  (CaO  56.0,  CO2  44.0  per  cent). 
GENERAL  DESCRIPTION.— Simple  or  pseudohexagonal  crystals. 


MINERALS   IMPORTANT  IN   THE  INDUSTRIES.        445 


Also  columnar  and  needle  masses,  oolitic,  stalactitic  and  coral-like. 
The  prevailing  tint  is  white,  but  the  color  is  occasionally  violet 
or  pale  green. 


FIG.  435.         FIG.  436. 


FIG.  437. 


FIG.  438. 


Bilin,  Bohemia. 


Herrengrund. 


CRYSTALLIZATION. — Orthorhombic.  Axes  a  :  b  :  c  =  0.622  :  i  : 
0.721.  Occasionally  simple  crystals,  Fig.  435,  with  acute  domes 
and  pyramids  such  as  e  =  (QO  a  :  b  :  6c),  {061 } ;  and  s  =  (fa  :  b  : 
6c),  {9.12.2}.  These  grade  into  needle-like  forms.  More  fre- 
quently twinned,  with  twin  plane  m,  giving  prisms  with  pseudo- 
hexagonal  cross  sections,  Figs.  437  and  438. 

Supplement  angles  are:  mm  =  63°  48';  dd  =  71°  33';  w  = 
130°  21';  ee  =  153°  57'. 

Physical  Characters.     H.,  3.5  to  4.     Sp.  gr.,  2.93  to  2.95. 

LUSTRE,  vitreous.  TRANSLUCENT  or  transparent. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  violet,  yellow,  pale  green. 

CLEAVAGE. — Parallel  to  brachy  pinacoid,  prism,  and  brachy  dome. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  colors  flame  red.  In  closed 
tube  decrepitates,  loses  weight  and  falls  to  pieces.  With  hydro- 
chloric acid,  dissolves  with  rapid  effervescence.  Powdered  and 
boiled  in  a  test-tube  with  dilute  cobalt  solution  aragonite  is  turned 
to  a  lilac  color. 

SIMILAR  SPECIES. —  Natrolite  and  other  zeolites  which  occur  in 
needle  crystals  do  not  effervesce  in  acids.  Strontianite  and  wither- 
ite  have  higher  specific  gravity  and  are  fusible.  Calcite  has  a 
lower  specific  gravity,  differs  in  form,  cleaves  in  three  directions 
with  equal  ease  yielding  a  rhombohedron  of  105°  5',  and  in 
powder  is  unaffected  when  boiled  with  cobalt  solution. 


446 


MINERALOGY. 


REMARKS. — Occurs  as  crystals  in  gypsum  and  clay,  as  at  Bastennes,  France,  and 
Molina,  Aragon,  and  in  the  sulphur  deposits  of  Sicily  and  the  lead  veins  of  Silesia. 
Coral  like  (flos  ferri)  or  fibrous  at  the  Styrian  and  Carinthian  iron  mines  and  the 
Organ  Mts.,  New  Mexico.  As  needles  in  hollows  of  basalt.  As  the  pearly  layer  of 
shells  and  the  material  of  coral. 

CALCITE. — Calcspar,    Limestone,    Marble,    Iceland    Spar,    Etc. 

COMPOSITION. — CaCOs,  (CaO  56.0,  CO2  44.0  per  cent.). 
GENERAL  DESCRIPTION. — Yellowish  white  to  white  or  colorless, 
more  or  less  transparent  crystals,  of  many  shapes,  all  of  which 


FIG.  439. 


FIG.  440. 


FIG.  441. 


will  cleave  to  a  rhombohedron  of  105°.  Cleavable,  coarse-  and 
fine-grained,  fibrous  and  loosely  coherent  masses.  Crusts,  stalac- 
tites. 

CRYSTALLIZATION.  —  Hexagonal.  Scalenohedral  class,  p.  48. 
Axis  <r  =  0.854. 

Occurs  in  many  forms,  of  which  the  most  common  are  the 
rhombohedra:  /,  the  unit;  e  =  (a  :  oo  a  :  a  :  fa\  {ioT2}  ;/= 
(a  :  co  a:  a:  2c\  {2021};  q  =  (a  :  oo  a  :  a  :  i6c\  {16.0.16.1}; 
scalenohedron  :  v  =  f  0  :  30  :  a  :  -$c,  {2131 }  and  unit  prism.  Twins 
are  frequent.  Supplement  angles  are//  =  74°  55'  ;  ee  =  45°  3' ; 
ff—  101°  9';  qq=  119°  24'.  The  polar  edges  w  are  75°  22' 
and  3 5°  36'. 

Optically  — .  With  very  strong  double  refraction,  but  weak  re- 
fraction (a  =  1.486  ;  f  =  1.658  for  yellow  light). 

Physical  Characters.     H.,  3.     Sp.  gr.,  2.71  to  2.72. 

LUSTRE,  vitreous  to  dull.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  yellow,  white,  colorless,  or  pale  shades  of  red,  green, 
blue,  etc. 

CLEAVAGE,  parallel  to  the  rhombohedron,  therefore  yielding  di- 
edral  angles  of  105°  5'  and  74°  55'. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        447 
FIG.  442.  FIG.  443.  FIG.  444. 


FIG.  445. 


FIG.  448. 


Dog  Tooth  Spar,  Geikie. 
FIG.  446. 


FIG.  449 


FIG.  450. 


FIG.  447. 


FIG.  451. 


BEFORE  BLOWPIPE,  ETC. — Infusible.  Becomes  opaque  and  alka- 
line and  colors  flame  red.  Soluble  readily  in  cold  dilute  acids, 
with  vigorous  effervescence. 

VARIETIES. — The  following  are  the  most  prominent  varieties . 

Iceland  Spar. — Colorless,  transparent  crystals  and  masses. 

Dog-  Tooth  Spar. — Scalenohedral  crystals,  supposed  to  resemble 
canine  teeth  in  shape. 

Fontainebleau  Sandstone. — Crystals  containing  up  to  60  per  cent, 
of  sand. 

Satin  Spar. — Fibrous,  with  silky  lustre. 


448  MINERAL  OGY. 

Argentine — Foliated,  pearly  masses. 

Marble. — Coarse  to  fine  granular  masses,  crystalline. 

Limestone. — Dull,  compact  material,  not  composed  of  crystalline 
grains. 

Chalk. — Soft,  dull-white,  earthy  masses. 

Calcareous  Marl. — Soft,  earthy  and  intermixed  with  clay.- 

Stalactites. — Icicle-like  cylinders  and  cones,  formed  by  partial 
evaporation  of  dripping  water. 

Stalagmite. — The  material  forming  under  the  drip  on  the  floor 
of  the  cavern. 

Travertine,  Qnyx. — Deposits  from  springs  or  rivers,  in  banded 
layers. 

Other  names,  such  as  Hydraulic  Limestone,  Lithographic  Lime- 
stone, Rock  Mealy  Plumbocalcite,  Spartaite,  etc.,  are  of  minor  im- 
portance, and  are  chiefly  based  on  color,  use,  locality,  etc.,  and 
do  not  generally  indicate  important  structural  or  chemical  dif- 
ferences. 

SIMILAR  SPECIES. — The  distinctions  from  aragonite  have  been 
given  under  that  mineral.  Dolomite  differs  in  slow  partial  solu- 
tion in  cold  dilute  acids,  instead  of  rapid  and  complete  efferves- 
cence. 

REMARKS. — Occurrence  and  uses  as  described  on  pp.  439  to  441  and  437. 

ANKERITE. 

COMPOSITION. — (Ca.Mg.Fe)CO3  sometimes  containing  manganese. 

GENERAL  DESCRIPTION.— Gray  to  brown  rhombohedral  crystals  like  those  of  siderite, 
also  cleavable  and  granular  masses  and  compact. 

PHYSICAL  CHARACTERS. — Translucent  to  opaque.  Lustre,  vitreous  to  pearly.  Color, 
gray,  yellow  or  brown.  Streak,  white  or  nearly  so.  H.,  3.5  to  4.  Sp.  gr.,  2.95  to  3.1. 
Brittle.  Cleavage,  rhombohedral.  R  f\  ^  =  106°  12'. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  darkens  and  becomes  magnetic.  Soluble  in 
acids  with  effervescence. 

DOLOMITE. — Pearl  Spar,  Magnesian  Limestone. 

COMPOSITION.  —  CaCO3.MgCO3  often  contains  iron  or  man- 
ganese. 

GENERAL  DESCRIPTION. — Small,  white,  pink  or  yellow,  rhombo- 
hedral crystals,  usually  with  curved  faces,  or  more  frequently 
white,  massive  marble,  with  coarse  to  fine  grain  ;  or  gray,  white  and 
bluish,  compact  limestone. 

CRYSTALLIZATION. — Hexagonal,  class  of  third  order  rhombohe- 
dron,  p.  54.  Axis  c  =  0.832.  Usually  the  unit  rhombohedron 


MINERALS   IMPORTANT  IN   THE   INDUSTRIES.        449 


FIG.  452. 


FIG.  453. 


/,  Fig.  464,  the  faces  curved  or  doubly  curved  (saddle-shaped). 
Often  made  up  of  smaller  crystals.  Sometimes  the  more  acute 
rhombohedron  r  =  (a  :  oo  a  :  a  :  4<r),  {4041}.  Supplement  angles 
are//=  73°  45'  ;  rr  =  113°  53'. 

Optically—,  with  even  stronger  double  refraction  than  calcite. 

Physical  Characters.     H.,  3.5  to  4.     Sp.  gr.,  2.8  to  2.9. 
LUSTRE,  vitreous  or  pearly.  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  pink,  greenish-gray,  brown  or  black. 
CLEAVAGE.     Rhombohedral.     Angles,  106°  15'  and  73°  45'. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  colors  flame  yellowish-red 
and  becomes  alkaline.  With  cobalt  solution,  becomes  pink. 
Fragments  are  very  slightly  attacked  by  cold  dilute  acid.  The 
powdered  mineral  is  sometimes  attacked  vigorously  by  cold  dilute 
acid,  but  sometimes  is  not.  On  heating  there  is  a  vigorous  effer- 
vescence. 

SIMILAR  SPECIES. — Differs  from  calcite  in  effervescence,  color 
with  cobalt  solution  and  frequent  curvature  of  rhombohedral 
planes.  It  differs  from  siderite  and  ankerite  in  not  becoming 
magnetic  on  heating. 

REMARKS. — Dolomite  is  frequently  the  chief  constituent  of  whole  mountain 
ranges  as  in  the  Tyrol  Alps  and  at  Eifel.  Formed  possibly  from  calcite  by  infiltration 
of  waters  containing  magnesium  carbonate.  Crystals  are  common  in  gypsum  and 
on  granular  dolomite  as  at  Hall,  Tyrol,  the  zinc  region  of  Missouri,  and  many  places 
in  the  limestone  region  of  Western  New  York. 

The  sugar  grain  structure  is  more  common  than  with  calcite  owing  to  better 
development  of  the  crystals. 

THE   MAGNESIUM   MINERALS. 

The  minerals  described  are : 
30 


450  MINERAL  OGY. 

Hydroxide  Brucite  Mg(OH)2  Hexagonal 

Sulphates  Kieserite  MgSO4.H2O  Orthorhombic 

Epsomite  MgSO^yHaO  Orthorhombic 

Carbonate  Magnesite  MgCOs  Hexagonal 

Most  of  the  magnesium  is  combined  with  the  great  silicates 
such  as  amphibole,  pyroxene,  biotite,  enstatite,  hypersthene, 
chrysolite,  serpentine,  and  talc,  and  the  double  salts  carnallite, 
kainite  and  dolomite. 

It  forms  also  borates  (boracite),  chlorides,  sulphates,  and  other  silicates  (fosterite, 
sepiolite,  chondrodite,  most  of  which  are  of  very  minor  importance.  The  alumin- 
ate  spinel  is  described. 

ECONOMIC   IMPORTANCE. 

The  world  produces  nearly  300,000  tons  of  crude  and  calcined 
magnesite  annually  of  which  two  thirds  comes  from  Austria- 
Hungary,  one  sixth  from  Greece  and  the  rest  chiefly  from  India 
and  the  United  States. 

The  United  States  used  in  1914  the  equivalent  of  132,000  short 
tons  of  calcined*  magnesite,  of  which  about  127,000  tons  was 
imported. 

The  minerals  economically  used  are  magnesite,  kieserite  and  also 
carnallite,  p.  418,  and  dolomite,  p.  447. 

Magnesite. 

A  use  for  the  uncalcined  material  is  said  to  be  as  a  substitute 
for  barite  in  paint.  Some  is  made  into  chloride  or  sulphate,  but 
nearly  all  is  calcined,  yielding  according  to  temperatures  used: 

(a)  Caustic  Magnesia   (moderate   temperatures),   with  3   to  8 
per  cent.  CO2  left.     In  this  state  it  will  combine  with  magnesium 
chloride  to  a  very  strong  "  oxychloride "  cement,  much  used  for 
sanitary  floors  in  buildings,  steel  cars,  etc.     Usually  "fillers"  of 
cork  asbestos,  etc.,  are  added. 

(b)  Dead-burned  Magnesia  (Incipient  Fusion^). — In  this  state 
will  not  slake  or  combine  with  chemicals  and  is  used  as  basic 
bricks  for  lining   Portland*   cement   kilns,   basic  steel   furnaces, 
kilns  for  sulphuric  acid  burning  and  electric  furnaces. 

*  One  ton  of  calcined  is  equivalent  to  about  2^  tons  of  crude, 
t  The  presence  of  6-8  per  cent,  of  iron  in  the  Austrian  material  helps  by  lowering 
fusion  point,  thus  giving  a  product  which  shrinks  less. 


MINERALS  IMPORTANT  IN  THE  INDUSTRIES.       451 

(c)  Carbon  dioxide  may  be  saved,  but  is  said  to  interfere  with 
proper  calcining. 

The  calcined  product  is  the  source  of  magnesium  bisulphite 
used  in  disintegrating  wood  for  wood  pulp  paper. 

Kieserite. 

Epsomite  or  epsom  salts  are  made  by  recrystallizing  the  Stass- 
furt  kieserite  (and  also  from  bitterns  and  by-products  in  other 
processes).     It  is  used  as  a  laxative  and  in  the  textile  industries 
(weighting  and  sizing  cotton  yarn)  and  as  a  fertilizer  for  clover 
hay. 

The  basic  carbonate  magnesia  alba  may  be  precipitated  from 
epsomite  or  kieserite  by  sodium  carbonate. 

Dolomite  is  calcined  in  large  amounts  in  Pennsylvania,  dis- 
solved and  the  "basic  carbonate,"  magnesia  alba,  precipitated 
and  used  as  a  fireproof  material  and  non  conductor  (for  steam 
pipes)  and  many  other  purposes. 

Carnallite  is  used  in  the  liquid  state  in  the  oxychloride  cement 
and  for  treating  cotton  goods. 

It  is  also  by  electrolysis  converted  into  metallic  magnesium, 
now  made  in  quantity  in  the  shape  of  ribbon  and  as  coarse  grains, 
and  used  in  flash  lights,  as  a  reducing  agent  in  the  preparation  of 
some  of  the  rarer  elements,  as  a  purifying  agent  to  remove  the 
last  traces  of  oxygen  from  copper,  nickel  and  steel  and  as  a  de- 
hydrating agent  for  certain  oils  and  for  alcohol.  The  metal  is 
steadily  increasing  in  commercial  importance. 

Carnallite  with  calcined  magnesite  is  used  as  a  fireproof  paint. 

FORMATION  AND  OCCURRENCE  OF  MAGNESIUM  MINERALS. 
The  commercially  important  deposits  of  magnesite  and  kieserite 
are  secondary,  the  magnesite  being  either  due  to  alterations*  of 
basic  eruptives  or  serpentine  in  veins  or  masses  in  the  rock  or  to 
metasomatic  replacement  of  limestone  or  dolomite  occurring  as 
beds;  the  kieserite  to  deposition  from  solutions  as  at  Stassfurt. 


*  Solutions  of  CO2  may  by  attack  on  chrysolite  produce  both  serpentine  and 
magnesite, 

Mg2SiO4  +  CO2  +  2H20  =  H4Mg2Si2Oa  +  MgCOa, 

or  by  attack  on  serpentine  produce  magnesite 

H4Mg3Si209  +  3C02  =  3MgC03  +  2H2O  +  2SiO2. 


452  MINERAL  OGY. 

Magnesite  in  Veins  or  Masses  in  Basic  Rocks  or  Serpentines. 

Usually  as  fine-grained  porcelain-like  material,  the  most  im- 
portant being  veins  in  Euboea,  Greece,  the  largest  50  to  60  feet 
thick  and  1,300  feet  long.  Other  deposits  worked  are  veins  in 
serpentine  at  Grochberg,  Silesia,  and  veins  in  Tulare,  San  Benito, 
and  Santa  Clara  Counties,  California.  The  magnesite  may  be  in 
granular  aggregates  disseminated  through  the  serpentinous  rocks. 

Magnesite  in  Beds  as  Metasomatic  Replacements. 

The  world's  great  sources  are  the  beds  in  Styria,  Austria,  re- 
sembling coarsely  crystalline  dolomite  with  some  siderite.  The 
largest  bed  at  Veitsch  is  a  huge  lens  700  to  800  feet  thick  and 
about  a  dozen  others  are  worked.  A  bed  associated  with  lime- 
stones in  the  Swiss  Tyrol  is  regarded  as  of  similar  origin,  and  the 
crystalline  beds  of  Canada  may  be  also  of  this  type. 

Kieserite  and  Epsomite  as  Saline  Residues. 

At  Stassfurt,  Prussia,  kieserite  constitutes  about  one  fifth  of  a 
layer  190  feet  thick,  chiefly  halite  and  carnallite,  and  is  one  of 
the  constituents  of  the  overlying  mixed  salts.  In  Albany  County, 
Wyoming,  are  several  lakes,  in  which  deposits  of  epsomite  are 
formed  on  a  very  large  scale. 

BRUCITE. 

COMPOSITION. — Mg(OH)2,    (MgO  69.0,  H2O  31.0  per  cent.). 

GENERAL  DESCRIPTION. — White  or  gray  translucent  foliated 
masses  with  pearly  or  wax-like  lustre.  Also  fibrous  and  in  tabular 
hexagonal  crystals. 

Physical  Characters.  H.,  2.5.  Sp.  gr.,  2.38  to  2.4. 

LUSTRE,  pearly  or  wax-like.  TRANSLUCENT. 

STREAK,  white.  TENACITY,  sectile  and  flexible. 

COLOR,  white,  bluish,  greenish.  CLEAVAGE,  basal. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  becomes  alkaline,  and  with 
cobalt  solution  becomes  pink.  Yields  water  in  closed  tube.  Solu- 
ble in  hydrochloric  acid. 

SIMILAR  SPECIES.— -Harder  and  more  soluble  than  foliated  talc 
or  gypsum,  and  quite  infusible. 

REMARKS. — Brucite  is  usually  found  in  serpentine  or  limestone  with  magnesite  or 
hydromagnesite.     On   exposure  it  becomes  coatee*  with  a  white  powder,  and  is  some 
times  changed  to  serpentine  or  hydromagnesite.  Its  most  prominent  American  locality 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        453 

is  at  Texas,  Pa.,  also  at  Fritz  Island  in  the  same  State;    at  Brewsters,  N.  Y..  and 
Hoboken,  N.  J. 

KIESERITE. 

COMPOSITION. — MgSO4  +  H2O,  MgO,  29.0,  SOs  58.0,  H2O  13  per  cent. 

GENERAL  DESCRIPTION. — Coarse  to  fine  granular  or  compact  masses  of  white  or 
yellowish  color.  Rarely  in  monoclinic  pyramids.  H.,  3  to  3  .5.  Sp.  gr.,  2.52  to  2.57. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily,  heated  on  coal  with  cobalt  solution 
becomes  pink.  Slowly  but  completely  soluble  in  water 

REMARKS. — As  stated  on  p.  452,  occurs  in  enormous  quantities  at  Stassfurt^ 
often  mixed  with  carnallite  and  other  salts.  Also  found  at  Hallstadt  and  Kalusez, 
Galicia. 

EPSOMITE.  —Epsom  Salt. 

COMPOSITION. -MgSO4-f7H2O,  (MgO  16.3,  SO3  32.5,  H2O  51.2  per  cent.). 

GENERAL  DESCRIPTION.  —  A  delicate  white  fibrous  efflorescence 
FiG.  454.  or  earthy  white  crust  with  a  characteristic  bitter  taste.     Also  com- 

mon in  solution  in  mineral  water.  Occasionally  in  crystals,  Fig. 
454,  which  are  noticeable  as  representing  class  of  the  sphenoid  in 
the  orthorhombic  system,  p.  41.  Optically  — . 

PHYSICAL  CHARACTERS.  —  Transparent  or  translucent.  Lustre, 
vitreous  or  dull.  Color  and  streak,  white.  H.,  2  to  2.5.  Sp.  gr., 
I  75.  Taste,  bitter  and  salt. 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  at  first,  but  becomes  infusible 
after  the  water  of  crystallization  has  been  driven  off.  With  cobalt 
solution  becomes  pink.  In  closed  tube  yields  acid  water.  Easily 
soluble  in  water. 

REMARKS.  —  Epsomite  is  formed  by  action  of  the  sulphuric  acid  of  decomposing 
sulphides,  upon  such  magnesian  minerals  as  serpentine  and  talc  and  in  considerable 
quantities  in  caves  in  limestone  as  at  Mammoth  Cave,  Kentucky  At  Epsom, 
England,  it  is  a  fibrous  efflorescence.  At  Stassfurt  it  occurs  in  granular  masses  due 
to  alteration  of  kieserite. 

MAGNESITE. 

COMPOSITION. — MgCO3,  (MgO  47.6,  CO2  52.4  per  cent.),  with 
sometimes  iron  or  manganese  replacing  part  of  the  magnesium. 

GENERAL  DESCRIPTION. — White  porcelain-like  masses  or  dense 
rounded  nodules  or  marble-like  with  coarse  grain.  Rarely  in 
crystals  like  those  of  siderite. 

Physical  Characters.     H.,  3.5  to  4.5.  Sp.  gr.,  3  to  3.12. 

LUSTRE,  dull,  vitreous  or  silky,  OPAQUE  to  translucent. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  yellow,  brown.  FRACTURE,  conchoidal. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  becomes  alkaline.  With 
cobalt  solution  becomes  pink.  Soluble  with  effervescence  in 
warm  hydrochloric  acid,  but  does  not  effervesce  in  cold  dilute 
acid.  No  decided  precipitate  is  produced  by  addition  of  sulphuric 


454  MINERAL  OG  Y. 

acid,  whereas  heavy  precipitates  form  with  solutions  of  calcite  and 
dolomite. 

SIMILAR  SPECIES. — Differs  from  dolomite  and  calcite  in  not 
yielding  the  calcium  flame. 

REMARKS. — Occurrences  and  uses  as  described  on  pp.  450,  452.  Other  localities 
in  America  are  Bolton  and  Sutton,  Province  of  Quebec,  at  Texas,  Pa.,  Barehills,  Md.f 
and  Bolton  and  Roxbury,  Massachusetts,  and  other  foreign  localities,  Madras,  India; 
Hrubschiitz,  Moravia;  Snarum,  Norway;  Greiner,  Tyrol. 

THE  BORON   MINERALS. 

THE  minerals  described  are  : 


Acid 

Sassolite 

H3B03 

Monoclinic 

Borates 

Borax 

Na2B4O7,  ioH2O 

Monoclinic 

Ulexite 

CaNaB6O8.8H,O 

Colemanite 

Ca2B6Oir5H20 

Monoclinic 

Boracite 

Mg.CLB^Oon 

Isometric 

Boron  is  also  a  constituent  of  the  silicates  tourmaline,  datolite, 
axinite  and  danburite,  and  of  a  number  of  rare  borates  such  as 
sussexite,  howlite,  and  warwickite. 

ECONOMIC   IMPORTANCE. 

The  world's  production*  is  about  120,000  tons  of  crude  ores, 
of  which  the  United  States  furnishes  about  half  in  the  form  of 
colemanite,  Chili  about  two  fifths  in  the  form  of  ulexite  and  Turkey 
14,000  tons  in  the  form  of  pandermite  (colemanite).  The  small 
production  of  Italy  (sassolite) ,  Peru,  Argentina  and  Bolivia  (ulexite) 
and  Germany  (boracite)  make  up  the  rest. 

In  1914  this  country  produced  62,400  tons,  all  colemanite  from 
California. 

Sassolite  to  the  extent  of  two  or  three  thousand  tons  yearly, 
is  obtained  by  condensing  and  evaporating  the  steam  issuing  from 
fumaroles  in  the  mountains  of  Tuscany. 

When  the  crude  material  is  borax  with  other  sodium  and  cal- 
cium salts,  the  borax  is  extracted  by  boiling  in  hot  water,  cooling 
and  crystallizing.  The  calcium  borates  are  decomposed  by  sodium 
carbonate  or  sulphate  to  form  borax,  or  by  sulphuric  or  hydro- 
chloric acid  or  chlorine  if  boric  acid  is  first  to  be  produced. 

Commercial  borax  is  manufactured  from  all  the  minerals  men- 

*  Mineral  Resources  U.  S.,  1914,  p.  285. 


MINERALS  IMPORTANT  IN   THE  INDUSTRIES.        455 

tioned,  and  has  important  uses.  Because  of  its  power  to  unite 
with  almost  any  oxide  to  form  a  fusible  compound  it  is  used  in 
blowpipe  analysis,  assaying,  soldering,  brazing  and  welding  and 
as  a  basis  of  enamels.  Because  of  its  cleansing  qualities  it  is 
used  in  soaps  and  cleansing  solutions,  and  because  of  its  antiseptic 
qualities  it  is  used  as  a  food  preservative,  and  in  antiseptic  powders 
and  cosmetics. 

It  is  a  constituent  of  flint  glass,  strass,  from  which  imitation 
gems  are  cut,  and  mixed  with  casein  it  forms  a  substance  resembling 
gum  arabic. 

FORMATION  AND  OCCURRENCE  OF  BORON  MINERALS. 
Boron  occurs  in  igneous  and  metamorphic  rocks,  contacts,  and 
fissures  as  borosilicates,  especially  tourmaline,  but  also  datolite, 
axinite  and  danburite.  The  economic  deposits,  however,  are 
borates  or  boric  acid,  which  appear  in  general  to  be  associated  with 
volcanic  exhalations. 

Vapors  of  Lagoons  (Soffioni). 

In  certain  of  the  steaming  lagoons  of  Tuscany  the  vapors  contain 
chiefly  boric  acid  (sassolite) .  This  is  true  of  some  other  volcanic 
vapors,  as  at  Vulcano,  Lipari. 

Hot  Springs  in  Volcanic  Regions. 

At  Sasso  and  Mt.  Rotondo,  Tuscany,  are  hot  springs  containing 
boric  acid  (sassolite).  A  copper  mine*  at  Boccheggiano,  Tuscany, 
had  to  be  abandoned  because  it  encountered  a  boric  acid  (sassolite) 
spring  at  a  temperature  of  40°  C.  A  hot  spring  at  Bafios  del  Toro, 
Chili,  deposits  calcium  borate,  colemanite^  and  the  hot  springs 
of  California  and  Nevada  and  Ladak  Kashmer,  India  and  the 
mud  volcanoes  of  Kertch  and  Taman,  southern  Russia,  deposit 
borax. 

Old  Lake  Beds. 

The  tertiary  lake  beds  of  California  yield  colemanite  in  large 
amounts.  They  occur  in  clay  and  sandstone  underlain  by  rhyolite 
and  overlain,  by  gypsum,  limestone  and  debris,  the  largest  being 
in  a  range  of  hills  near  Death  Valley  and  the  solid  mineral  being 

*  Beyschlag,  Vogt  and  Krusch  (Truscott),  911. 
t  Lindgren,  "Mineral  Deposits,"  277. 


456  MINER  ALOG  Y. 

at   times  in  layers   15   feet   thick.     The  Turkish   deposits   near 
Panderma,  Asia  Minor,  similarly  lie  in  a  bed  beneath  gypsum. 

Lindgren*  holds  that  during  the  formation  of  the  lake  beds  there  was  also  intense 
volcanic  activity  and  large  volumes  of  hot  water  containing  boron,  which  in  contact 
with  limestone  or  solutions  containing  calcium  produced  the  colemanite-. 

Borax  Lakes  or  Marshes. 

The  original  borax  locality  was  the  shores  of  the  salt  lakes  of 
Tibet.  In  California,  Nevada  and  Oregon  borates  occur,  chiefly 
borax  and  ulexite,  in  the  marshes  and  "playas,"  or  shallow  nearly 
dry  lakes,  probably  leached  from  the  higher  colemanite  deposits. 
Similar  deposits,  chiefly  ulexite,  occur  in  lagoons  and  troughs  in 
Atacama  and  Ascotan,  Chili;  also  in  Argentina  and  Peru  with 
gypsum  and  halite. 

Marine  Borates. 

The  borates  deposited  from  sea  water  are  chiefly  boracite  as 
at  Stassfurt  and  the  crystals  in  gypsum  in  other  localities. 

SASSOLITE.  —  Natural  Boracic  Acid. 

COMPOSITION.  —  H3BO3,  (B2O3  56.4,   H2O 43. 6  per  cent). 

GENERAL  DESCRIPTION.  —  Small  white  or  yellowish  scales,  of 
pearly  lustre,  acid  taste,  and  somewhat  unctuous  feel.  Rarely 
stalactitic  or  in  minute  triclinic  crystals.  Occurs  chiefly  in  solu- 
tion or  vapor  in  volcanic  regions. 

Physical  Characters.     H.,  I.     Sp.  gr.,  1.43. 

LUSTRE,  pearly.  TRANSLUCENT. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white  or  yellowish.  TASTE,  sour  or  acid. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  with  intumescence  to  a 
clear  glass  without  color,  but  colors  the  flame  yellowish-green.  In 
closed  tube,  yields  water.  Soluble  in  water. 

REMARKS. — In  the  region  of  volcanoes  sassolite  is  brought  to  the  surface  in  the  jets 
of  steam,  collects  in  the  water  from  these  jets,  and,  to  some  extent,  forms  also  a  crust 
more  or  less  solid.  The  only  productive  locality  is  in  Tuscany.  It  forms  a  small 
proportion  of  the  boron  compounds  at  the  California  borax  localities. 

BORAX.— Tinkal. 

COMPOSITION.— Na2B4O7.  i  oH2O,  (B2O3  36.6,  Na2O  16.2,  H2O 
47.2  per  cent.). 

*  Ibid.,  282. 


MINERALS  IMPORTANT  IN   THE  INDUSTRIES.        457 

GENERAL  DESCRIPTION. — A  glistening,  white  or  nearly  white 
efflorescence  or  constituent  of  certain  soils,  but  more  frequently 
in  solution  in  lakes,  or  as  well-formed  monoclinic  crystals  in  the 
mud  of  these  lakes.  The  crystals  closely  resemble  those  of  py- 
roxene in  form  and  angle. 

Physical  Characters.     H.,  2  to  2.5.     Sp.  gr.,  1.69  to  1.72. 
LUSTRE,  vitreous  to  dull.  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  gray,  bluish,  greenish.  TASTE,  alkaline. 

BEFORE  BLOWPIPE,  ETC. — Swells  greatly  and  fuses  to  a  clear 
glass.  Colors  flame  yellow,  and  if  mixed  to  a  paste  with  a  flux 
of  acid  potassium  sulphate  and  powdered  fluorite,  and  fused,  it  will 
color  the  flame  bright  green.  In  closed  tube,  swells,  blackens, 
yields  much  water  and  a  burnt  odor.  Soluble  in  water.  If  treated 
with  a  few  drops  of  sulphuric  acid,  covered  with  alcohol,  and  the 
alcohol  set  on  fire,  a  green  flame  is  obtained. 

REMARKS. — Occurs  as  described  on  p.  456,  as  a  deposit  from  lakes  and  mud 
volcanoes.  In  the  United  States  the  deposits  are  mainly  in  Esmeralda  County, 
Nevada,  and  in  Lake,  Bernardino  and  Inyo  Counties,  California. 

ULEXITE.— Boronatrocalcite.     * 

COMPOSITION.— CaNaB5O9.8H2O,  (B2O3  43A  CaO  13.8,  Na2O 
7.7,  H2O  35.5  per  cent). 

GENERAL  DESCRIPTION. — White,  rounded  masses  (cotton-balls) 
of  loosely-compacted,  intertwined,  silky  fibres,  which  are  easily 
pulverized  between  the  fingers. 

Physical  Characters.     H.,  I.     Sp.  gr.,  1.65. 

LUSTRE,  silky.  TRANSLUCENT. 

COLOR  and  STREAK,  white.  TENACITY,  brittle. 

BEFORE  BLOWPIPE,  ETC. — Fuses  very  easily,  with  intumescence 
to  a  clear  glass.  Colors  flame  intense  yellow,  and  will  yield  green 
flame,  as  with  borax.  In  closed  tube  yields  water.  Soluble  in 
acids. 

REMARKS. — Occurs  in  dry  lakes  or  on  the  banks  surrounding  partially  dried  lakes, 
with  halite,  gypsum,  glauberite,  borax,  etc.,  as  described  on  p.  456;  also  in  small 
amount  in  the  gypsum  of  Nova  Scotia. 


458 


MINERALOGY. 


FIG.  455. 


COLEMANITE.  —  Priceite,  Pandermite. 

COMPOSITION.  —  Ca2B6On  +  sH2O,  (B2O3  50,9,  CaO  27.2,  H2O 
21.9  per  cent). 

GENERAL  DESCRIPTION.  —  Occurs  in  groups  of  colorless  trans- 
parent crystals  resembling  those  of  datolite  but  usually  larger,  and 
in  simpler  wedge-shaped  forms.  Also  found  in 
compact  white  masses  like  porcelain  and  in 
loosely  aggregated  chalk-like  masses. 

CRYSTALLIZATION.  —  Monoclinic.  Axes  a  :  ~b 
:c  =  0.775  :  i  :  0.541  ;  ft  =  69°  51'.  Common 
faces  are  :  /  =  (20  :  b  \  cor),  {  1  20}  ;  v  =  (a  :  b  : 
2c\  {221};  e  =  (coa  :  b  :  2c),  {021};  h  =  (a  :  oo 
b  :  2c\  {201}.  Usually  short  prismatic  and 
highly  modified.  Supplement  angles,  mm  =  72° 


4'  ; 


73°  49'  J 


69°  5  1'. 


Physical  Characters.     H.,  4  to  4.5.     Sp.  gr.,  2.26  to  2.48. 
LUSTRE,  vitreous  to  dull.         TRANSPARENT  to  opaque. 
STREAK,  white.  TENACITY,  brittle. 

COLOR,  white  or  colorless.        CLEAVAGE,  parallel  clino-pinacoid 

Before  Blowpipe,  Etc.  —  Decrepitates,  intumesces  and  fuses 
easily  to  white  or  colorless  glass,  coloring  the  flame  green.  In- 
soluble in  water,  easily  soluble  in  hot  hydrochloric  acid  with 
separation  of  boric  acid  on  cooling.  Strongly  heated  with  cobalt 
solution  becomes  blue. 

VARIETIES.  Priceite.  —  Loosely  compacted  white  chalky  masses. 
Pandermite.  —  Firm  compact  porcelain-like  white  masses. 

REMARKS.  —  Priceite  occurs  in  Curry  County,  Oregon,  in  layers  between  slate  and 
steatite.  Pandermite  is  found  in  a  bed  beneath  gypsum  near  Panderma  on  the  Sea  of 
Marmora.  Colemanite  at  Inyo  and  San  Bernardino  Counties,  Cal.  ,  with  celestite  and 
quartz.  Especially  abundant  near  Daggett  in  the  Mojave  Desert. 


BORACITE. — Stassfurtite. 

COMPOSITION.  —Mg7Cl2B,6O30  (B2OS  62.57,  MgO  31.28,  Cl  7.93  per  cent.). 

GENERAL  DESCRIPTION.  —  Snow-white,  rather  soft  masses  ( Stassfurtite)  and  small 
hard  glassy  isometric  crystals  of  the  hextetrahedral  class,  p.  62,  usually  showing  the 
tetrahedron  /  with  or  without  the  cube  a  and  dodecahedron  d  Strongly  pyroelectric. 

PHYSICAL  CHARACTERS.  . —  Transparent  to  opaque.  Lustre,  vitreous.  Color,  white, 
yellowish,  greenish.  Streak,  white.  H.,  7  (crystals),  4.5  (masses).  Sp.  gr.,  2.9  to  3. 
Brittle. 


MINERALS   IMPORTANT  IN   THE   INDUSTRIES.        459 
FIG.  456.  FIG.  457. 


0 

a- 

V 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  with  intumescence,  to  a  white  glass  and 
colors  the  flame  yellowish  green.  In  closed  tube  yields  no  water  or  but  little.  Solu- 
ble slowly  in  hydrochloric  acid.  Strongly  heated  with  cobalt  solution  becomes  violet. 

REMARKS.  —  Occurs  in  deposits  of  halite,  gypsum,  anhydrite,  and  especially  in  the 
immense  beds  of  potassium  and  magnesium  salts  at  Stassfurt,  Prussia. 

MINERALS  OF  CHLORINE,  BROMINE,  IODINE,  FLUORINE. 

Chlorine  occurs  in  the  igneous  basic  rocks  in  sodalite, 
wernerite,  chlor-apatite.  It  is  rare  in  ore  veins,  though  the 
chlorides  of  silver  and  mercury  may  occur  in  upper  parts  of 
deposits.  The  economic  sources  are  the  chlorides  of  the  chemical 
sediments  and  brines,  especially  halite,  carnallite,  kainite,  sylvite. 

Halite  is  the  usual  raw  material.  By  treatment  with  sulphuric 
acid  hydrochloric  acid  is  made  and  chlorine  from  hydrochloric 
acid  and  pyrolusite.  Calcium  chloride  to  the  amount  of  20,000 
tons  per  year  is  recovered  from  brines  in  the  U.  S. 

Bromine. 

Aside  from  bromyrite,  and  embolite,  and  the  rare  iodobromite 
there  are  no  recognized  minerals  containing  bromine.  The  ele- 
ment occurs  in  the  minerals  of  the  chemical  sediments  especially 
at  Stassfurt,  Germany,  where  the  mother  liquors  carry  15  to  35 
per  cent.  Br.  The  brines  of  the  Saginaw  Valley  in  Michigan,  in 
the  Ohio  Valley  in  Ohio  and  West  Virginia,  and  in  the  Kanawah 
Valley  in  West  Virginia  contain  2  to  3  parts  of  bromine  to  1 ,000 
of  salt,  which  after  the  crystallization  of  the  salt,  is  recovered. 

The  production*  of  bromine  in  the  United  States  in  1915  was 
855»857  pounds,  valued  at  $856,307. 

Bromine  is  used  in  making  the  bromides  for  medicine  and  pho- 
tography, and  in  coal-tar  dyes  and  as  a  disinfectant.  The  recent 

*  Min.  Resources,  U.  S.,  1915,  p.  276. 


460  MINER  ALOG  K 

large  demand  from  abroad  is  said  to  be  for  making  asphyxiating 
gases. 

Iodine. 

There  are  few  mineral  species  which  contain  iodine,  those  best 
known  are :  the  iodides  of  silver  and  copper,  iodyrite  and  mar  shite, 
and  the  iodate  lautarite*  Ca  I2O6  found  in  the  sodium  nitrate 
deposits  of  Chili. 

The  great  source  of  iodine  is  the  mother  liquor  from  the  refining 
of  soda  niter,  which  may  contain  as  much  as  20  per  cent,  of  sodium 
iodate.  It  is  treated  with  sodium  bisulphite  giving  solid  iodine 
which  is  filtered  and  sublimed. 

There  was  produced  in  1913 — 961,336  pounds  of  which  this 
country  used  288,750  in  the  manufacture  of  iodoform,  hydriodate 
and  potassium  iodide. 

Fluorine. 

The  fluorine  minerals  are  connected  with  pneumatolytic  action, 
contacts,  pegmatites,  tin  and  apatite  veins,  etc.  The  great 
minerals  are  fluorite,  and  cryolite,  but  it  enters  into  various 
silicates  such  as  topaz,  chrondrodite,  lepidolite  and  some  tourma- 
line and  into  pyrochlore,  fluocerite  and  a  series  of  unimportant 
fluorides. 

The  principal  product  is  hydrofluoric  acid  made  from  fluorite 
(or  cryolite)  and  used  in  etching  glass  and  as  a  preservative. 

THE   SULPHUR   MINERALS. 

The  mineral  described  is: 
Element  Sulphur  S  Orthorhombic 

The  great  sulphides,  pyrite,  marcasite,  pyrrhotite,  sphalerite, 
galenite,  chalcopyrite,  and  many  minor  sulphides,  sulpho  salts 
and  sulphates  such  as  gypsum,  anhydrite,  barite,  have  already 
been  described. 

ECONOMIC   IMPORTANCE. 

The  United  States  consumed  approximately!  1,000,000  long 
tons  of  sulphur  in  1914.  Of  this  amount  324,627  tons  was  in  the 

*  Large  colorless  to  yellow  monoclinic  crystals  often  in  a  band  of  gypsum.     Easily 
soluble  in  hydrochloric  acid  with  evolution  of  Cl. 
t  Mineral  Industry,  1914,  pp.  685,  689,  701. 


MINERALS  IMPORTANT  IN   THE  INDUSTRIES.^       461 

form  of  native  sulphur,  almost  wholly  obtained  from  Louisiana, 
607,496  tons  was  present  in  pyrite  from  which  it  was  burned, 
and  175,000  tons  were  recovered  in  sulphuric  acid  from  the 
sulphides  of  zinc  and  copper  during  the  recovery  of  the  metals. 

Deducting  the  sulphur  from  imported  pyrite  and  brimstone 
and  adding  the  exported  sulphur  the  net  sulphur  produced  in  the 
United  States  in  1914  becomes 

Sulphur  in  native  sulphur 324,627 

Sulphur  in  pyrite 148,131 

Sulphur  in  sulphuric  acid 175,000 


647,758  tons 

Sulphur  is  also  recovered  in  large  quantities  from  the  former 
waste  products  of  gas  works,  Leblanc  soda  factories  and  other 
chemical  works. 

Nearly  one  half  of  the  world's  supply  of  native  sulphur  is  ob- 
tained from  the  Island  of  Sicily.  338,344  long  tons  were  produced 
in  1914. 

Sulphur  is  extracted  from  the  native  mineral  by  simple  fusion 
and  consequent  separation  from  the  gangue.  The  common  method 
in  use  in  Sicily  involves  the  burning  of  part  of  the  sulphur  to  melt 
the  remainder,  causing  heavy  loss  of  the  element.  The  crude  sul- 
phur may  be  refined  by  sublimation.  Pyrite  is  burned  directly  in 
specially  constructed  furnaces,  the  sulphur  dioxide  produced  being 
used  partly  as  such  but  most  of  it  being  converted  into  sulphuric 
acid  by  further  oxidation  sometimes  in  lead-lined  chambers  with 
steam  and  nitrous  fumes.  Most  of  the  sulphuric  acid  made  is 
"chamber  acid"  of  50  Baume  used  in  the  manufacture  of  fertilizers 
from  phosphate  rock,  making  ammonium  sulphate,  etc.  Stronger 
acid  is  used  for  "pickling"  steel  and  in  the  purification  of  petro- 
leum and  the  fuming  acid  in  the  manufacutre  of  explosives  and 
colors. 

Sulphur  dioxide  is  concentrated  and  liquefied  by  compression 
and  used  in  enormous  quantities  in  digesting  wood  pulp  for  paper 
stock  and  as  a  bleaching  agent  for  silk,  straw,  etc. ;  also  in  cleaning 
clay,  as  a  disinfectant  and  many  other  purposes.  Another  large 
use  of  sulphur  is  in  protecting  grape  vines  from  mildew,  especially 
in  France,  and  small  amounts  are  utilized  in  the  manufacture  of 


462     ,  MINERALOGY. 

matches — for  medicinal  purposes,  and  in  the  making  of  gunpowder, 
fireworks,  insecticides,  for  vulcanizing  india  rubber,  etc. 

FORMATION   AND    OCCURRENCE   OF   SULPHUR    DEPOSITS. 

Disregarding  sulphur  derived  by  alteration*  of  sulphides,  pyrite, 
galenite,  etc.*  Sulphur  deposits  classify  as : 

Sulphur  from  Volcanic  Exhalations. 

Resulting  from  partial  oxidation  of  H2S  or  reaction  between 
H2S  and  SC>2  given  off  from  volcanoes  and  depositing  in  fissures 
and  elsewhere  in  the  crater. 

The  most  important  deposit  is  at  Hokkaido,  Japan,  in  walls 
and  massive  heaps  in  an  old  crater  still  yielding  fumes.  Another 
not  yet  worked  is  at  Popocatapetl,  Mexico,  and  a  deposit  exists 
on  a  volcanic  island  near  New  Zealand. f  Smaller  deposits  exist 
in  the  Yellowstone. 

Deposits  from  Hot  Springs. 

Superficial  deposits  due  to  oxidation  of  H2S  exist  near  hot 
springs, J  some  of  which  are  workable,  as  at  Cody,  Wyoming; 
Cove  Creek,  Utah;  Cuprite,  Nevada;  and  Sulphur  Bank,  Cali- 
fornia. 

In  Gypsum  of  Chemical  Sediments. 

Nearly  all  great  gypsum  beds  contain  sulphur  and  nearly 
all  great  sulphur  beds  occur  with  gypsum  and  limestone  associated 
with  hydrocarbons,  carbonates  and  sulphates.  It  is  practically 
certain  the  sulphur  is  due  to  the  reduction  of  gypsum  by  organic 
agencies. 

The  most  important  deposits  are  those  of  Sicily  and  Louisiana. 

In  Sicily  the  sulphur-bearing  gypsum  carrying  8  to  25  per  cent. 
S  is  with  blue  gray  limestone,  clay,  sandstone  and  halite.  At 
Calcasieu,  Louisiana,  almost  100  feet  of  pure  sulphur  underlies 
clay  and  limestone.  Other  localities  in  which  S  was  derived 
from  beds  of  gypsum  are  Texas;  Conil  near  Cadiz,  Spain;  Bex, 
Switzerland;  Cracow,  Poland. 


*  The  pyrite  in  limestone  of  Lake  Champlain  sometimes  yields  crusts  of  sulphur 
an  inch  thick. 

t  Mineral  Industry,  1914,  p.  689. 

\  Lindgren,  "Mineral  Deposits,"  338. 


MINERALS   IMPORTANT  IN   THE   INDUSTRIES.        463 


SULPHUR.  — Brimstone. 

COMPOSITION.  —  S,  sometimes  with  traces  of  tellurium,  selenium, 
or  arsenic.  Often  mixed  with  clay  or  bitumen. 

GENERAL  DESCRIPTION.  —  Translucent  or  transparent,  resinous, 
crystals  of  characteristic  yellow  color.  Also  in  crusts,  stalactites, 
spherical  shapes,  and  powder.  Sometimes  brown  or  green. 


FIG.  458. 


FIG.  459. 


CRYSTALLIZATION. — Orthorhombic.  Axes£  :<5:r  =  o.  813:1: 
1.903.  Usually  the  pyramid/,  sometimes  modified  by  the  base  c, 
the  pyramid  s  =  (d  :  b  :  %  r),  { 1 1 3 }  ;  or  the  dome  d  =  (  oo  d  :  b  :  c), 
{on}.  Supplement  angles //  =  73°  34'  ;  ss  =  53°  9';  cd=  62° 
if. 

Optically  + .  Axial  plane,  the  brachy-pinacoid.  Acute  bisec- 
trix vertical.  Axial  angle  with  yellow  light  2V '=  69°  5'. 

Physical  Characters.     H.,  1,5  to  2.5.     Sp.  gr.,  2.05  to  2.09. 
LUSTRE,  resinous.  TRANSPARENT  to  translucent. 

STREAK,  white  or  pale  yellow.  TENACITY,  brittle. 
COLOR,  yellow,  yellowish-orange,  brown,  or  gray, 
CLEAVAGE,  parallel  to  base,  prism  and  pyramid,  not  perfect. 

BEFORE  BLOWPIPE,  ETC. — Melts  easily,  then  takes  fire  and  burns 
with  a  blue  flame  aud  suffocating  odor  of  sulphur  dioxide.  In 
closed  tube  melts  and  yields  a  fusible  sublimate,  brown  hot,  yellow 
cold,  and  if  rubbed  on  a  moistened  silver  coin  the  coin  is  blackened. 
Insoluble  in  acids. 


REMARKS. — Occurrence  and  uses,  as  described  on  p.  461-462. 


464  MINER ALOG  Y. 

THE   SELENIUM   AND   TELLURIUM   MINERALS. 

The  mineral  described  is: 

Tellurium  Te,  Hexagonal 

Native  selenium  is  not  proved.  Selensulphur  is  a  name  given 
to '  selenium-bearing  sulphur  from  Vulcano,  Lipari,  Sandwich 
Islands  and  Japan.  Several  selenides*  occur  including  selenides 
of  mercury,  tiemanite,  and  onofrite,  and  selenide  of  lead, 
clausthalite. 

Selenium. 

Selenium  in  minute  quantities  occurs  in  the  copper  ores  of  Butte, 
Montana,  and  other  copper  regions.  22,867  pounds  was  recovered 
in  1914  from  their  electrolytic  refining. f  It  is  also  found  in  the 
gold  bullion  from  Tonopah,  Nevada,  and  Redjang  Lebong, 
Sumatra.  In  none  of  these  cases  have  the  selenium  minerals 
been  identified. 

Selenium  is  used  principally  to  give  a  red  color  to  the  glass 
used  in  signal  lamps  and  to  color  enamels  red.  According  to 
Roscoe  and  SchorlemmerJ  selenium  heated  for  considerable  time 
to  210°  C.  attains  a  granular  condition.  In  this  condition  if  ex- 
posed to  diffused  daylight  its  electric  resistance  diminishes  in- 
stantly and  on  shutting  off  light  it  slowly  regains  it.  A  number 
of  electrical  inventions  depend  on  this,  such  as  automatic  lighting 
and  extinguishing  gas  buoys.  Selenium  cells  for  measuring  the 
intensity  of  light  have  been  constructed.  Minor  uses  are  in  micro- 
scopic and  chemical  work. 

Tellurium. 

Tellurium  occurs  plentifully!  in  combination  with  gold,  silver, 
mercury,  lead  and  bismuth  as  the  minerals  calaverite,  sylvanite, 
krennerite,  hessite,  petzite,  nagyagite,  coloradoite,  tetradymite. 
Oxidized  products  are  rare.|| 

*  Rarer  species,  naumannite,  berzelianite,  lehrbachite,  eucairite,  zorgite,  crookesite. 

f  Mineral  Resources  U.  S.f  1914,  p.  13. 

%  "Chemistry,"  Vol.  I,  p.  462. 

§  Rarer  tellurides  are  altaite,  stutzite,  tapalpite.  It  has  been  estimated  th'^t  at  the 
Cripple  Creek  locality  the  weight  of  tellurium  exceeds  that  of  the  gold  approximately 
in  the  ratio  7  to  5;  that  is,  with  a  gold  production  of  up  to  1908  of  $191,830,000 
there  has  been  about  450  tons  of  tellurium. 

l|  Tellurite,  emmonsite,  durdenite. 


MINERALS   IMPORTANT  IN   THE   INDUSTRIES.        465 

Although  found  in  the  slimes  of  the  copper  refineries  there  are 

no  economic  uses. 

TELLURIUM. 

COMPOSITION. — Te  with  a  little  Se,  S,  Au,  Ag,  etc. 

GENERAL  DESCRIPTION. — A  soft  tin  white  mineral  of  metallic  lustre  occurring  fine 
grained  or  in  minute  hexagonal  prisms. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  metallic.  Color  and  streak,  tin-white. 
H.,  2  to  2.5.  Sp.  gr.,  6.1  to  6.3.  Rather  brittle. 

BEFORE  BLOWPIPE,  ETC. — On  charcoal  fuses  easily,  volatilizes,  coloring  flame 
fjreen  and  forming  a  white  coat,  which  is  made  rose  color  by  transferring  to  porcelain 
and  moistening  with  sulphuric  acid.  Soluble  in  hydrochloric  acid. 

REMARKS. — Occurs  at  Zalathna,  Siebenburgen,  in  sandstone,  sprinkled  through 
pyrite  or  alternating  with  it  in  thin  layers;  at  the  John  Jay  mine,  Colorado,  in  pieces 
up  to  25  pounds,  and  in  California. 

THE  HYDROGEN  MINERALS. 

The  mineral  described  is: 

Water.  H2O,  Hexagonal. 

HYDROGEN,  which  forms  about  one  per  cent,  of  the  earth's  crust, 
is  a  constituent  of  many  minerals,  being  present  in  combination 
and  as  water  of  crystallization.  It  is  present  to  a  limited  extent 
in  natural  gas  and  in  volcanic  gases;  it  escapes  in  combination  with 
sulphur  from  many  sulphur  springs  and,  in  combination  with  car- 
bon, occurs  as  marsh  gas,  petroleum,  ozocerite,  etc. 

Its  compound  water  is  everywhere  in  nature  and  the  great  part 
it  plays  in  the  formation  and  decomposition  of  minerals  has  been 
discussed,  p.  244.  It  is  a  universal  solvent  when  pure. 

The  uses  are  too  well  known  to  need  summarizing  even  if  sta- 
tistics were  available.  The  minor  item  of  mineral  waters  in  1914 
amounted  to  54,358,466  gallons  and  the  yearly  supply  of  water 
for  one  great  city  probably  exceeds  in  weight  the  yearly  production 
of  any  other  mineral  product  in  the  entire  country. 

WATER.  — Ice,  Snow. 

COMPOSITION. —  H2O,  (H.,  n.i,  O.,  88.9  per  cent). 

GENERAL  DESCRIPTION. —  Ice  or  snow  at  or  below  o°  C.  Water 
from  o°  to  1 00°  C.  Steam  above  100°  C.,  or  aqueous  vapor  at 
all  ordinary  temperatures. 

CRYSTALLIZATION. — Hexagonal.    Axis  c  =  1.403  approximately. 

As  snow,  the  crystals  are  principally  compound  star-like  forms 
branching  at  60°  and  of  great  diversity.  Simple  crystals  are 
sometimes  found  as  hail.  Optically  -f. 


466 


MINERALOGY. 


FIG.  460. 


FIG.  461. 


FIG.  462. 


FIG.  463. 


Magnified  Snow  Crystals. 

Physical  Characters.     H.  (ice),  1.5.     Sp.  gr.  (ice),  0.91. 
LUSTRE,  vitreous.  TRANSPARENT. 

STREAK,  colorless.  TENACITY,  brittle. 

COLOR,  white  or  colorless,  pale  blue  in  thick  layers. 
Tasteless  if  pure. 

BEFORE  BLOWPIPE,  ETC. — Melts  at  o°  C.  Under  pressure  of 
760  mm.  boils  at  100°  C.  and  is  converted  into  steam. 

THE   NITROGEN   MINERALS. 

The  two  great  nitrates,  soda  nitre  and  nitre,  have  been  de- 
scribed and  their  occurrence  and  importance  discussed.  Other 
minor  nitrates  exist,  one  of  which,  nitrocalcite,  Ca(NO3)2  +  wH2O, 
is  not  uncommon  as  an  efflorescence  in  limestone  caves  and  it  is 
stated*  that  in  the  war  of  1812  the  material  from  Mammoth 
Cave,  Kentucky,  was  leached  and  converted  into  nitre  by  filtering 
through  wood  ashes.  Nitrocalcite  is  also  found  in  the  soil  of 
Venezuela.  A  few  still  rarer  nitrates  are  known,  such  as  darap- 
skite  and  gerhardtite,  others  have  been  reported  and  nitrogen  is 
found  in  uraninite. 

The  necessity  of  nitrogenous  compounds  for  plant  food  and  for 
explosives  has  resulted  in  successful  attempts  to  fix  atmospheric 
nitrogen  by  the  arcf  calcium  cyanamide  and  Haber  methods, 
and  to  further  utilize  the  ammonium  sulphate  produced  in  coking 

*  Merrill's  "Rock-forming  Minerals,"  p.  318. 

t  In  the  production  of  calcium  cyanamide,  coke  and  lime  are  fused  together  to 
form  calcium  carbide.  This,  when  heated,  is  treated  with  pure  nitrogen  made  at 
the  present  time  by  liquifying  air  and  boiling  off  the  oxygen.  In  the  arc  method 
the  nitrogen  and  oxygen  of  the  air  are  directly  combined  under  the  influence  of  the 
electric  discharge.  In  the  Haber  process  nitrogen  and  hydrogen  are  made  to  com- 
bine under  pressure  at  elevated  temperatures  in  the  presence  of  some  catalyzing 
agent. 


MINERALS  IMPORTANT  IN   THE  INDUSTRIES.       467 

and  estimated*  as  about  700,000  tons  per  year.     A  process  for 
oxidizing  this  ammonia  to  nitric  acid  is  still  needed. 

THE   PHOSPHORUS   MINERALS. 

The  minerals  described  are. 

Apatite  Ca5(Cl.F)(PO4)3  Hexagonal 

Wagnerite  Mg2PO4F  Monoclinic 

Wavellite  A16(OH)6(PO4)4  +  pH2O  Orthorhombic 

Vivianite  Fe3(PO4)2  8H2O  Monoclinic 

Phosphides  exist  in  iron  meteorites,  but  otherwise  phosphorus 
occurs  only  in  the  form  of  phosphates,  of  which  there  are  known 
about  fifty,  including  xenotime,  monazite,  pryomorphite,  amblygon- 
ite,  lazulite,  variscite,  turquois,  torbernite,  and  autunite. 

ECONOMIC   IMPORTANCE. 

The  yield  of  crystalline  apatite  is  nearly  negligible  and  the 
phosphorite  deposits  of  Spain  are  no  longer  worked.  There  may 
be  some  recovery  of  such  material  as  a  by-product  in  the  concen- 
tration of  the  iron  ores  of  New  York  and  Norway. 

Practically  the  economic  deposits  are  limited  to  rock  phosphates 
and  guanos. 

In  1915  this  country  produced f  1,835,667  long  tons  of  phosphate 
rock  distributed  as  follows : 

Florida 1,358,611 

Tennessee  and  Arkansas 3  89, 7  59 

South  Carolina 83,460 

Idaho,  Utah  and  Wyoming 3.83? 

The  world's  production  in  1913  amounted  to  over  6,780,000 
metric  tons.  In  1914  there  was  a  heavy  decline  to  less  than 
4,000,000  tons.J  This  country  produced  over  one  half  and  the 
other  great  producers  were  Tunis  and  Algeria  both  working 
"bone"  phosphates. 

There  is  a  small  use  for  making  phosphorus,  but  the  principal 
use  is  as  phosphates  for  fertilizers.  A  considerable  amount  is 
ground  raw  and  used  directly,  but  the  greater  part  is  converted 
into  soluble  phosphates  by  treatment  with  sulphuric  acid,  in  which 
state  it  is  more  readily  available  as  plant  food. 

*  Gilbert,  Publication  2421  Smithsonian  Inst. 
t  Minerals  Res.  U.  S.,  1915,  advance  sheets. 
J  Mineral  Industry,  1914,  p.  585. 


468  MINERAL OG  Y. 

FORMATION   AND    OCCURRENCE    OF   PHOSPHATES. 

Phosphorus  is  present  in  the  crust  of  the  earth  to  the  amount 
of  about  one  tenth  of  one  per  cent.  In  the  form  of  apatite  and  to 
a  much  less  extent  monazite  and  xenotime  it  is  widely  distributed 
as  minute  crystals  in  igneous  rocks. 

The  economic  deposits  may  be  grouped  under  several  heads. 
Magmatic  Segregations. 

The  great  apatite-iron  deposits  of  Gellivare  and  Kiirunavaara, 
Norway,  are  magmatic  segregations*  consisting  of  magnetite  with 
considerable  fluor --apatite. 

Veins. 

Veins  the  material  of  which  is  believed  to  have  been  pneuma- 
tolytically,  p.  242,  extracted  from  the  neighboring  gabbro  by 
hydrochloric  acid  and  deposited  there  as  chlorapatite  while  at  the 
same  time  the  plagioclase  of  the  country  rock  has  been  converted 
into  scapolite,  occur  at  Oeddegadenf  Bamle,  Norway,  and  along 
the  coast  at  Langesund,  Snarum,  Arendal,  etc.  Associated  are 
large  crystals  of  wagnerite  and  enstatite  and  there  is  abundant 
rutile,  ilmenite  and  pyrrhotite.  The  original  gabbro  contained 
0.65  P2O5  14  to  1.5  HC1. 

Similar  conditions  prevailt  with  the  Canada  veins  which  are  in 
close  association  with  a  gabbro  (pyroxenite).  The  apatite  is  fluor 
apatite  with  a  little  chlorine;  there  is  no  enstatite  but  some  augite, 
biotite,  scapolite,  calcite,  titanite,  and  ilmenite. 

Apatite  is  a  constant  associate  of  tin  veins,  as  at  Ehrenfriedensdorf,  Zinnwald, 
Cornwall,  Devonshire,  South  Dakota,  but  is  practically  never  in  lead,  silver,  zinc 
or  gold  veins. 

The  formerly  important  deposits  of  fibrous  concretionary  apatite  or  phosphorite 
of  Estramadura,  Spain,  occur  in  16  foot  quartz  veins  in  clay  slate  in  and  near  granite 
and  at  Jumilla,§  Spain,  there  is  a  basic  eruptive  of  sanidine  and  leuctte  with  a  net- 
work of  veins  rich  in  apatite. 

Secondary  Phosphates. 

Some  of  the  weathering  solutions  due  to  the  decomposition  of 
apatite  react  with  other  decomposition  products  producing  secon- 
dary phosphates.]] 

*  Beyschlag,  Vogt  and  Krusch  (Truscott),  173. 

t  Ibid.,  175.  453- 

t  Ibid.,  454- 

§  Beyschlag,  Vogt  and  Krusch  (Truscott),  452. 

||  Especially  phosphates  of  iron  and  aluminum  such  as  Iron.  Vivianite,  du- 
frenite,  strengite,  etc.  Aluminum.  Wavellite,  turquoise,  variscite,  etc.  Of  these 
vivianite  is  common  in  bog-iron  ore. 


MINERALS   IMPORTANT  IN  THE   INDUSTRIES.        469 

The  greater  portion  of  the  phosphoric  acid  in  the  weathering 
solutions  reaches  the  soil  or  the  sea  and  is  taken  up  by  plant  and 
animal  organisms,  from  which  there  result  beds  of  guano,  fossil 
bones  and  marine  deposits  of  bone,  shell  and  animal  matter,  all 
of  which  may  undergo  further  alterations. 
Marine  Sediments. 

When  the  -marine  organism  dies  the  remains,  shells,  fishes 
bones  and  teeth,  etc.,  collect  in  the  ooze  at  the  bottom  and  by 
relatively  more  rapid  solution  of  the  carbonates  may  form  phos- 
phate nodules  or  oolitic  beds  and  if  these  deposits  become  land 
may  be  still  further  concentrated  by  further  leaching  out  of  the 
carbonates  as  in  the  pebble  rock  deposits  of  the  coasts  and  rivers 
of  North  and  South  Carolina  or  may  be  essentially  unaltered* 
as  in  the  great  new  deposits  of  Idaho  and  Utah  where  the  phosphate 
shales  and  oolitic  beds  occur  near  the  center  of  a  great  formation 
in  beds  200  feet  thick,  or  may  present  both  stages  as  in  western 
Tennessee,  where  there  are  found  both  brown  residual  phosphates 
due  to  leaching  of  phosphatic  limestones  and  blue  or  black  oolitic 
and  shaly  beds. 

Other  important  marine  deposits  exist  in  Tunis  and  Algeria 
and  the  large  deposits  of  phosphate  are  derived  chiefly  or  entirely 
from  marine  deposits  and  are  chiefly  Ca3  (PO4)2,  but  are  said  to 
contain  more  fluorite  as  the  geologic  age  increases,  the  purest  ap- 
proaching fluor  apatite. 
Guano  Beds. 

Guano  beds  are  formed  by  sea  birds  in  rainless  regions,  as  on 
the  islands  near  Chili  and  Peru,  and  are  sometimes  100  feet  in 
depth  and  average  over  twenty  per  cent,  of  phosphate  and  even 
more  of  ammonia  salts. 

By  leachingt  some  deposits  have  lost  their  ammonia  salts,  as 
at  Navassa  and  Sombrero  and  others  of  the  West  Indies. 

Christmas  Island,  Indian  Ocean,  is  a  large  producer  and  others 
are  in  Polynesia. 
Replacements. 

GuanoJ  may  furnish  solutions  of  phosphates  capable  of  attacking 

*  Lindgren,  "  Mineral  Deposits,"  p.  260. 
t  Lindgren,  "Mineral  Deposits,"  p.  257. 

%  Guano  contains  many  phosphates,  some  of  which  are  acid.  Clarke  gives 
'Bulletin  491  U.  'S.  Geol.  Survey,  496,  a  list  of  10  species. 


470 


MINERALOGY. 


underlying  rocks,  forming  phosphate  of  lime  with  limestone  or 
phosphates  of  aluminum*  from  the  feldspars  of  igneous  rocks, 
as  in  the  trachyte  of  Clipperton  Atoll,  North  Pacific. 

Similarly  the  marine  sediment  phosphates,  may  be  in  part  dis- 
solved and  replace  limestone,  as  in  the  "white  phosphate"  of 
Tennessee. 

APATITE.— Asparagus  Stone.     Phosphate  Rock. 

COMPOSITION.— Ca6(Cl.F)(POJ3, 

GENERAL  DESCRIPTION. — Large  and  small  hexagonal  prisms, 
usually  of  green  or  red  color,  but  sometimes  violet,  white  or  yellow. 
Also  in  compact  varieties  which  are  commonly  dull-gray  or 
white,  rock-like  masses  or  nodules  not  unlike  common  limestone. 


FIG.  464. 


FIG.  465. 


FIG.  466. 


FIG.  467. 


Paris,  Me.  Zillerthal. 

CRYSTALLIZATION.  —  Hexagonal.  Class  3  °  order  pyramid,  p.  57. 
Axis  c  =  0.735.  Usually  the  unit  prism  m  terminated  by  the  unit 
pyramid  p  with  or  without  the  base  c.  More  rarely  the  second 
order  prism  a  or  the  flat  pyramid  o  =  (a  :  co  a  :  a  :  y2c\  {ioF2}, 
Fig.  469  ;  and  occasionally  third  order  pyramids,  as  t  =  ($a  :  A,a  : 
«:£:),  {3143},  Fig-  469- 


Supplement  angles  :  pp 


37°  44'; 


rr=22 


=  40°  18' 


cr=  22°  59'.     Optically  — ,  low  refraction,  weak  double  refraction. 

*  A  species  called  minervite,  approximating  H2KAl2(PO4)s6H2O,  has  been  found 
in  the  Minerva  Grotto,  France,  and  similar  material  from  Oran  Cave,  Algeria, 
Jenolan  Cave,  New  South  Wales.  Ibid.,  497. 


MINERALS  IMPORTANT  IN   THE  INDUSTRIES.        471 

Physical  Characters.     H.,  4.5  to  5.     83.,  gr.,  3.17  to  3.23. 

LUSTRE,  vitreous  to  resinous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  green,  red,  brown,  yellow,  violet,  white,  colorless. 

CLEAVAGE,  imperfect  basal  and  prismatic. 

BEFORE  BLOWPIPE,  ETC. — Fuses  with  difficulty  on  sharp  edges 
and  colors  the  flame  yellowish-red,  or,  if  moistened  with  concen- 
trated sulphuric  acid,  colors  the  flame  momentarily  bluish-green. 
Easily  soluble  in  hydrochloric  acid. 

If  to  ammonium  molybdate  in  nitric  acid  solution  a  few  drops 
of  a  nitric  acid  solution  of  apatite  be  added,  a  bright-yellow  pre- 
cipitate will  be  thrown  down  on  heating.  In  the  chlorine  variety 
silver  nitrate  will  produce  a  curdy  white  precipitate  in  the  nitric 
acid  solution. 

VARIETIES. — Certain  mineral  deposits  are  essentially  of  the  same 
composition  as  crystalline  apatite. 

Phosphorite. — Concretionary  masses,  with  fibrous  or  scaly  struc- 
ture. H  =  4.5. 

Phosphate  Rock.— Approaches  Ca3  (PO4)2;  sometimes  is  only 
phosphatized  limestone,  shale,  etc. ;  usually  marine  sediment. 

Guano. — Granular  to  sponge-like  and  compact  material,  of  gray 
to  brown  color.  Sometimes  with  lamellar  structure. 

SIMILAR  SPECIES. — Green  crystals,  differ  from  beryl  in  lustre, 
hardness  and  solubility.  Red  crystals  differ  from  willemite  in 
not  gelatinizing  or  yielding  zinc. 

REMARKS. — Occurs  as  described  on  p.  468.  The  most  famous  American  localities 
for  the  pure  mineral  are  in  Ontario  and  Quebec,  Canada.  *  Others,  smaller  in  extent, 
occur  at  Bolton,  Mass.;  Crown  Point,  N.  Y.,  and  Hurdstown,  N.  J. 

WAGNERITE. 

COMPOSITION. — Mg2PC>4F,  P2O5  43.8,  MgO  49.3,  F  u.8  per  cent. 

GENERAL  DESCRIPTION. — Cleavable  masses  and  rough  monoclinic  crystals  of 
yellow  to  flesh  red  color.  H.,  5  to  55.  Sp.  gr.,  2.98. 

BEFORE  BLOWPIPE. — Fuses  at  4  to  greenish  gray  glass.  With  sulphuric  acid 
gives  bluish  flame.  In  closed  tube  with  phosphorus  glass  gives  fluorine.  Soluble 
in  hydrochloric  acid. 

REMARKS. — The  dominant  mineral  in  some  of  the  phosphate  veins  of  Bamle, 

Norway. 

WAVELLITE. 

COMPOSITION. — A16(OH)6(PO4)4  +  9H2O,  (Al2Os  38.0,  P2O5  35.2,  H2O  26.8  per 
cent.).  F  is  sometimes  present. 

GENERAL  DESCRIPTION. — Hemispherical  masses  which,  when  broken,  yield  com- 
plete or  partial  circles  with  radiating  crystals,  rarely  large  enough  to  be  measured. 


472  MINERAL  OGY. 

Occasionally  stalactitic.     Color  most  frequently  white,  green  or  yellow.     H.,  3.5  to  4. 
Sp.  gr.,  2.31  to  2.34. 

BEFORE  BLOWPIPE,  ETC. — Whitens,  swells,  and  splits,  but  does  not  fuse.  With 
cobalt  solution  becomes  deep  blue.  In  closed  tube  yields  acid  water.  Soluble  in 
hydrochloric  acid.  Ammonium  molybdate  produces  a  yellow  precipitate  from  nitric 
acid  solutions. 

REMARKS. — A  secondary  mineral  chiefly  in  clays  and  fractures.  In  the  United 
States  is  most  abundant  at  Magnet  Cove,  Ark.,  Holly  Springs,  Pa.,  where  it  was 
used  for  manufacture  of  phosphorus,  and  Silver  Hill,  N.  C. 

Foreign  localities  are  Barnstaple,  Devonshire;  Dillenburg,  Nassau;  Cerhovic, 
Bohemia. 

VIVIANITE.— Blue  Iron  Earth. 

COMPOSITION —Fe3(PO4)2  -f  8H2O.    (FeO  43.0,  P2O6  28.3,  H2O  28.7  per  cent.). 

GENERAL  DESCRIPTION. — Usually  found  as  a  blue  to  bluish  green  earthy  mineral, 
often  replacing  organic  material  as  in  bones,  shells,  horn,  tree  roots,  etc.  Also  found 
as  glassy  crystals  (monoclinic),  colorless  before  exposure,  but  gradually  becoming 
blue. 

PHYSICAL  CHARACTERS. — Transparent  to  opaque.  Lustre,  vitreous  to  dull.  Color 
and  streak,  colorless  before  exposure,  but  usually  blue  to  greenish.  H=l.5  to  2. 
Sp.  gr.,  =  2.58  to  2.69.  Brittle. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  to  a  black  magnetic  mass  and  colors  flame 
pale  bluish-green,  especially  after  moistening  with  concentrated  sulphuric  acid.  In 
closed  tube  yields  water.  Soluble  in  hydrochloric  acid.  The  dried  powder  is  brown. 
REMARKS. — Common  with  bog  iron  ore.  Occurs  earthy  in  peat  moss  as  in  Shet- 
land or  near  tree  roots,  or  with  horns  of  the  elk,  Isle  of  Man,  as  crystals  with  pyrrhotite 
(Bodenmais)  or  pyrite  (Cornwall),  or  radiating  aggregates  often  within  fossil  shells 
(Crimea  and  Mullica  Hill,  N.  J.). 

THE   CARBON   MINERALS. 

The  more  definite  minerals  described  are : 

Graphite  C  Hexagonal 

Ozoceritf  CnH2n+2 

In  addition  to  these  there  are  a  large  number  of  gaseous,  liquid 
and  solid  carbon  compounds,  of  economic  importance  which  are 
on  the  border  line  of  mineralogy,  occurring  naturally  but  being 
generally  without  definite  composition  or  crystalline  form.  Among 
these  the  following  are  briefly  described:  PETROLEUM,  ASPHALT, 
MINERAL  COAL,  COPALITE,  and  AMBRITE. 

Other  carbon  minerals  elsewhere  described  are  diamond,  and  amber.  Carbon 
also  exists  in  enormous  quantities  in  the  mineral  carbonates  such  as  calcite, 
dolomite,  magnesite,  cerussite,  siderite,  and  aragonite  and  in  a  number  of  hydro- 
carbons, chiefly  paraffins  and  resins,  some  of  which  are  very  definite  in  composition 
and  may  even  be  crystalline,  but  are  economically  unimportant  such  as 
Scheererite  CH4  Monoclinic 

Hatchettite  C  :  H  =  i  :  i  Sometimes  crystals 

Fichtelite  C5H8  Monoclinic 

Hartite  Cu-Hia  Monoclinic 


MINERALS   IMPORTANT  IN   THE   INDUSTRIES,        473 
ECONOMIC   IMPORTANCE. 

From  this  standpoint  the  carbon  minerals  surpass  all  others 
both  in  quantities  used  and  values.  Of  the  $2,114,946,024  valua- 
tion placed  upon  the  mineral  products  of  the  United  States,  for 
1914  $895,615,858  are  for  coal  and  petroleum,  an  amount  ex- 
ceeding the  combined  value  of  the  production  of  all  the  metals. 

Graphite. 

In  1915  the  output  of  crystalline  graphite  in  the  mines  of  this* 
country  was  3,537  tons.*  Amorphous  graphite  to  the  extent  of 
1,1 8 1  tons-was  also  produced.  The  total  product  of  the  world  is 
over  100,000  tons  annually,  obtained  mainly  from  Ceylon  and 
Austria,  of  which  13,821  tons  was  imported  into  the  United  States 
in  1915. 

About  one  half  the  graphite  is  used  in  the  making  of  crucibles, 
the  dust  and  the  amorphous  material  are  used  chiefly  for  stove 
polish,  foundry  facings  and  paints,  and  the  other  large  uses  are 
electrical  purposes,  making  lead  pencils  and  lubricants.  Minor 
uses  are  in  electrotyping  and  in  protecting  various  products 
against  moisture,  especially  gunpowder,  but  also  tea  leaves,  coffee 
beans,  and  even  fertilizers. 

Ozocerite  is  mined  in  Hungary  and  Utah  and  in  1914  the 
United  States  imported!  over  4,000  tons  but  mined  none.  In  the 
crude  state  it  serves  as  an  insulator  for  electric  wires.  By 
distilling  it  yields:  a  refined  product,  ceresine,  used  for  candles, 
waxed  paper  and  hydrofluoric  acid  bottles;  burning  oils;  parafiine; 
a  product  with  properties  and  appearance  of  vaseline ;  and  a  black 
residuum  which  in  combination  with  india  rubber  constitutes  the 
insulating  material  called  okonite. 
Petroleum. 

The  production  of  crude  petroleum  in  the  United  States  in 
1914  was  265,762,535^:  barrels.  The  world's  production  was 
400,483,489  barrels.  This  country  therefore  producing  over  66 
per  cent,  of  all  while  Russia  produced  less  than  17  per  cent,  and 
no  other  country  except  Mexico  (5.29  per  cent.)  as  much  as  five 
per  cent. 

*  Mineral  Resources  U.  S.,  1915,  p.  82. 
t  Mineral  Resources  U.  S.,  1914,  p.  356. 
%  Mineral  Industry,  1914,  p.  568. 


474  MINERALOG  Y. 

Large  amounts  of  petroleum  in  the  crude  state  and  all  the 
distilled  heavy  oils  for  which  there  is  no  market  are  used  as 
"fuel  oils"  and  a  smaller  amount  of  special  oils  for  lubricating 
purposes.  Its  chief  value  is  due  to  its  distillation  products,  mainly 
kerosene.  Other  valuable  products  arising  from  distillation  of 
this  crude  oil  are  gasoline,  naphtha,*  benzene.  Various  products 
such  as  lubricating  oils,  vaseline  and  paraffine  are  made  from  the 
residuum  after  the  burning  oils  have  been  distilled  off. 

Asphalts. 

This  country  produced!  and  manufactured  from  petroleum  in 
1915  740,254  tons  of  asphalt  as  follows: 

Bituminous  rock 44.329 

Gilsonite  and  Wurtzilite 20,559 

Grahamite 10,863 

Manufactured  asphalt 664,503 

In  addition  to  which  it  imported  chiefly  from  Trinidad  and 
Venezuela,  180,689  tons  of  asphalt. 

The  world's  production  is  probably  about  400,000  tons  of  asphalt 
and  600,000  tons  of  bituminous  rock,  Trinidad  and  Venezuela 
furnishing  over  one  half  of  the  former  and  France  and  Italy  most 
of  the  latter. 

The  principal  use  is  for  pavements  of  streets  and  roads,  mixed 
with  sharp  sand,  limestone,  and  a  little  coal-tar  residuum.  They 
are  also  used  as  cement,  roofing  and  floor  material,  as  a  paint 
and  waterproofing  for  wood  or  metal,  for  insulating  electric  wires, 
and  as  an  adulterant  and  coloring  material  in  rubber  goods. 
Manjak  and  gilsonite  are  important  constituents  of  black  var- 
nishes. A  product  called  "ichthyol"  is  used  externally  and 
internally  in  medicine,  derived  from  a  bituminous  rock  full  of 
fossil  fish  at  Seefeld,  Tyrol. 

Fossil  Resins. 

The  fossil  resins  copalite  and  ambrite  do  not  occur  in  the  United 

States.      They  are  oxidized  hydrocarbons  much  resembling  ordi- 

. — — • — • — ' — , • 

*  Gasoline  is  also  obtained  from  natural  gas.  In  1914  to  the  amount  of  42,652,632 
gallons  with  little  loss  in  the  value  of  the  gas.  The  natural  gas  yield  in  1914  was 
valued  at  $94,115,524.  It  consists  essentially  of  marsh  gas,  but  also  contains 
hydrogen,  nitrogen  and  some  other  gases,  and  is  used  in  immense  quantities  as  a  fuel 
and,  after  being  enriched,  for  illuminating  purposes,  and  is  also  burned  to  produce 
lamp  black. 

t  Mineral  Resources  U.  S.,  1915,  p.  140. 


MINERALS  IMPORTANT  IN  THE  INDUSTRIES.        475 

nary  resin  in  appearance,  and  are  extensively  used  in  varnishes 
and  japans. 

Mineral  Coal. 

The  world's  production  of  mineral  coal  in  1914  was  1,226,330,612 
metric  tons,  of  which  three  countries  produced  86  per  cent,  as 
follows : 

United  States 517,285,050  or  47  per  cent. 

Great  Britain 292,047,544  "  24    " 

Germany 191,511,154  "   15    " 

The  estimated  production  in  the  U.  S.  for  1915  is  518,000,000 
tons. 

FORMATION  AND  OCCURRENCE  OF  THE  CARBON  MINERALS. 

With  the  exception  of  diamond  and  some  varieties  of  graphite 
the  carbon  minerals  are  of  undoubted  organic  origin,  due  to  former 
plant  and  animal  life.  Graphite  is  not  necessarily  so,  as  is  proved 
by  its  presence  in  meteorites  and  cast  iron. 

Separation  from  Magma.* 

Graphite  occurs  in  the  Disco  Island  iron,  p.  266,  which  contains 
up  to  four  per  cent,  of  carbon,  partly  as  graphite.  It  occurs  also 
in  pegmatites  and  nepheline  syenites. 

Metamorphosed  Sediments. 

Graphite  results  from  the  alteration  of  the  carbonaceous  matter 
in  the  sediment.  Occurrences  are  numerous  both  of  flake  or 
crystallized  graphite  as  in  Alabama  and  Pennsylvania,  and  of 
the  so-called  amorphous  graphite  as  in  California.  Considerable 
graphite  is  found  in  the  famous  Witwatersrand  conglomerate  and 
is  said  to  be  of  later  formation,  sometimes  replacing  the  quartz. 

Contacts. 

GRAPHITE  resulting  from  the  intrusion  of  igneous  rocks  may  be 
of  definitely  organic  origin  as  in  the  case  of  the  altered  coal  beds, 
at  Raton,  New  Mexico;  Sonora,  Mexico,  and  Styria,  in  which  the 
intermediate  stages  from  coal  to  graphite  are  present. 

In  other  instances  it  is  attributed  to  magmatic  exhalations,  for 
instance : 

*  Mineral  Industry,  1914,  p.  131. 

t  Lindgren,  "  Mineral  Deposits,"  p.  699.  Beyschlag,  Vogt  and  Krusch  (Truscott), 
p.  1161. 


476  MINERAL  O-G  Y. 

• 

"  The  graphite  gneiss  of  Passau  contains  the  mineral  as  a  secon- 
dary impregnation  only  at  the  contact  with  granite"*  and  speaking 
of  the  graphites  of  Quebec  "The  conclusion  is  justified  that  they 
were  developed  by  igneous  emanations  shortly  after  the  close  of 
intrusive  activity,  "f 

.Contacts  occur  also  at  Ticonderoga. 

Veins. 

Graphite  occurs  in  veins  in  igneous  rocks  and  the  surrounding 
sediments,  as  at  Ceylon,  in  fine-grained  gneiss  intruded  by  granites 
and  pegmatites.  Dillon,  Montana,  along  contact  of  pegmatitic 
granite  with  schists  and  limestone.  Near  Ticonderoga,  New  York, 
in  similar  contact.  The  Alibert  mines  of  Irkutsk,  Siberia,  in 
nepheline  syenite.  The  Borrowdale,  Cumberland,  in  porphyry. 

The  origin  is  puzzling  and  variously  ascribed  to  igneous  exhala- 
tions,! infiltration  of  liquid  hydrocarbons  and  subsequent  meta- 
morphism  and  to  gaseous  compounds  derived  from  the  adjoining 
sediments.  § 

It  is  of  interest  that  graphite  occurs  in  considerable  quantity 
in  the  silver  veins  of  Silver  Islet  ||  and  to  a  less  extent  in  the  silver 
veins  of  Temiskaming. 

Sedimentary. 

Mineral  coal,  asphaltum,  petroleum  and  ozocerite  are  all  of 
organic  origin.  The  coals  are  sediments  from  wood  grown  in 
place  or  carried  there  by  currents,  the  petroleum  and  asphalt  are 
chiefly  found  in  clay  shales,  sands,  sandstones  and  limestones  and 
the  ozocerite  is  a  derivative  of  petroleum. 

GRAPHITE.  — Plumbago,  Black  Lead. 

COMPOSITION. — C.     Sometimes  with  iron,  sand,  clay,  etc. 

GENERAL  DESCRIPTION. — Disseminated  flakes  or  scaly  to  com- 
pact masses,  and  more  rarely  six-sided  plates.  Soft,  greasy  and 
cold  to  the  touch ;  black  to  very  dark  gray  in  color  and  usually 
metallic  in  lustre.  When  impure  it  is  apt  to  be  slaty  or  earthy. 

*  Weinschenck,  "Grundziige  der  Gesteinskunde,"  p.  319. 

fLindgren,  "Mineral  Deposits,"  p.  704. 

J  "Grundziige  der  Gesteinskunde,"  p.  319,  320. 

§  Lindgren,  "Mineral  Deposits,"  p.  700. 

II  Beyschlag,  Vogt  &  Krujch  (Truscott),  p.  669. 


MINERALS  IMPORTANT  IN   THE   INDUSTRIES.        477 

Physical  Characters.     H.,  I  to  2.     Sp.  gr.,  2.09  to  2.25. 
LUSTRE,  metallic  to  dull.  OPAQUE. 

STREAK,  dark-gray.  TENACITY,  scales  flexible, 

COLOR,  black  or  dark  gray.  slightly  sectile. 

CLEAVAGE,  basal,  cleaves  into  plates.       UNCTUOUS,  marks  paper. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  but  is  gradually  burned. 
May  react,  if  impure,  for  water,  iron  and  sulphur.  Insoluble  in 
acids.  If  a  piece  of  graphite  is  brought  into  contact  with  a  piece 
of  zinc  in  a  solution  of  copper  sulphate,  it  is  quickly  copper-plated. 
Molybdenite  under  the  same  test  is  very  slowly  plated. 

SIMILAR  SPECIES. — Differs  from  molybdenite  in  darker  color, 
streak,  flame  test  and  salt  of  phosphorus  bead,  and  as  above  men- 
tioned. Micaceous  hematite  is  harder  and  has  a  red  streak. 

Graphite  is  distinguished  from  amorphous  carbon  by  treatment 
with  strong  oxidizing  agents  (KC1O3  and  HNO3),  by  which  it  is 
converted  into  graphitic  acid,  Ou^Oi,  a  yellow  transparent 
substance. 

REMARRS. — The  occurrence  and  uses  have  been  described  on  pp.  475  and  473. 

OZOCERITE   OR   MINERAL   WAX. 

COMPOSITION. — Closely  C.,  85.5,  H.,  14.5,  per  cent.  Essentially  one  of  the  higher 
members  of  the  paraffin  series,  CnH2n+2. 

GENERAL  DESCRIPTION. — Resembles  wax  in  appearance  and  consistency,  usually 
brown  to  nearly  black  and  foliated,  sometimes  with  greenish  opalescence,  which 
it  imparts  to  its  solutions.  H.,  about  2.  Sp.  gr.,  0.93  to  0.95. 

BEFORE  BLOWPIPE,  ETC. — Melts  at  51°  to  63°  C.  Soluble  in  ether,  naphtha  or 
turpentine,  partially  soluble  in  boiling  alcohol. 

REMARKS. — Ozocerite  is  regarded  as  a  derivative  of  petroleum.  Originally  found 
in.Slanik,  Moldavia,  then  in  larger  quantities  in  Boryslaw,  Galicia,  and  Emery  and 
Uinta  Counties,  Utah;  Baku,  Persia,  and  other  localities. 

PETROLEUM. — A  mixture  of  liquid  hydrocarbons.  The  American  oils  consist 
essentially  of  hydrocarbons  of  the  paraffine  series,  CnH2n+2,  with  smaller  amounts 
of  the  series  CnH2n  and  CnH2n-e.  The  Russian  oil,  obtained  mainly  from  Baku, 
on  the  Caspian,  and  the  oils  from  Rangoon,  Galicia,  are  different  in  character, 
consisting  mainly  of  the  naphthenes  CnH2n  and  do  not  yield  as  much  illuminating  oil 
on  distillation. 

The  German  petroleum  is  intermediate  and  the  Canadian  is  rich  in  the  solid 
paraffins. 

GENERAL  DESCRIPTION. — It  varies  from  a- light  easily  flowing  liquid  to  a  thick 
viscous  oil.  Usually  dark  brown  or  greenish  in  color  with  a  distinct  fluorescence. 
Sp.  gr.,  0.6  to  0.9. 

REMARKS. — Occurs  usually  in  clay,  shales,  sands,  sandstones  and  limestones  and 
in  cavities  to  which  it  has  penetrated  from  the  adjoining  rocks. 


478  MINERAL  OGY. 

ASPHALTUM  OR  MINERAL  PITCH.— Mixtures  of  different  hydrocarbons 
and  their  oxidized  products. 

GENERAL  DESCRIPTION. — Varying  from  thick,  highly  viscous  liquids  to  solids, 
generally  black  in  color  and  with  a  pitch-like  luster.  Melt  usually  from  35°  to  40°  C. 
and  burn  easily  with  a  pitchy  odor  and  bright  flame.  They  are  slightly  heavier  than 
water.  Trinidad.  Sp.  gr.,  1.28. 

REMARKS. — Asphaltum  includes  the  true  ASPHALT  of  the  famous  pitch  lakes  of 
Trinidad  and  of  Bermudez,  Venezuela  and  the  Dead  Sea;  the  MANJAK  of  Barbadoes; 
the  elastic  ELATERITE,  of  Derbyshire,  England;  the  ALBERTITE  of  New  Brunswick; 
the  GILSONITE  and  WURTZILITE  of  Utah,  the  GRAHAMITE  of  Oklahoma.  Besides 
these  sandstone  and  limestone  impregnated  with  asphalt  occur. 

MINERAL   COAL. 

GENERAL  DESCRIPTION. — Mineral  coal  is  a  compact  massive  material  of  black  or 
brownish  black  color  and  submetallic  to  earthy  lustre.  It  is  without  crystalline 
structure  or  cleavage  and  has  a  conchoidal  fracture.  H.,  0.5  to  2.5.  Sp.  gr.,  i.  to 
1.8. 

BEFORE  BLOWPIPE,  ETC. — Infusible  but  burns  and  may  become  pasty  and  in 
closed  tube  yield  oily  and  tarry  materials.  Insoluble  in  acids,  alcohol,  ether,  etc. 

VARIETIES. — The  entire  series  would  range  from  peat  to  anthracite.  Kemp 
giving*  as  typical  compositions 

O  N 

43  i 

33  2 

25  0.8 

13  0.8 

2.5  trace 

The  differences  in  appearance  are  great,  ranging  through  the  brown  spongy  peat, 
the  brownish  black  lignite,  the  compact  brown  to  black  bituminous  and  the  bright 
submetallic  black  anthracite. 

COPALITE  or  Highgate  Resin  from  the  London  blue  clay  and  copal  found  in 
the  soil  of  the  African  coast  are  pale  yellow  to  gray  or  dirty  brown  resins.  H.,  about 
3.  Sp.  gr.,  i.oi.  Giving  aromatic  odor  when  broken.  It  is  soluble  with  difficulty 
in  alcohol  and  turpentine  and  is  very  valuable  for  varnishes. 

AMBRITE  OR  DAMMAR.— A  fossil  resin  from  New  Zealand  resembling 
Kauri  gum  of  the  same  locality  and  of  the  East  Indies,  the  Moluccas  and  from  New 
Zealand.  It  is  not  so  hard  as  copal  but  is  harder  than  resin.  It  is  a  valuable  basic 
constituent  of  varnishes.  The  New  Zealand  dammar  is  almost  wholly  fossil 

*  "Hand-book  of  Rocks,"  p.  104. 


Woody  tissue  .... 
Peat  

C 

50 
59 

H 
6 
6 

Lignite  
Bituminous  coal  .  . 
Anthracite.  . 

69 
82 
.    OS 

5-5 
5 
2.=; 

CHAPTER  XX. 

SILICA  AND  THE  ROCK-FORMING   SILICATES. 

The  order  of  discussion  is  by  groups  of  chemically  or  genetically 
related  species.  The  economic  discussion  begins  the  chapter  but 
the  discussions  of  Formation  and  Occurrence  and  of  Optical 
Determination  precede  the  individual  groups. 

ECONOMIC   IMPORTANCE. 

Aside  from  the  occasional  occurrence  of  certain  silicates  in 
specimens  suitable  for  gems,  only  a  few  of  this  greatest  group  of 
common  minerals  are  of  economic  importance  as  distinct  minerals. 

The  Quarry  Industry. 

The  great  stone  or  quarry  industry*  represents  in  the  United 
States  a  capital  of  over  $125,000,000,  and  produced  in  1914 
material  worth  in  the  rough  over  $77,000,000,  and  consists  in  the 
extraction  of  blocks  of  either  limestone  and  marble  or  of  silica 
and  silicates.  The  values  of  silicate  rocks  quarried  in  this 
country  were : 

Granite $20,028,910 

Basalt  and  Related  Rocks 7.865,998 

Sandstone 7,501,808 

Bluestone 1,086,699 

Slate 5,706,787 

GRANITE,  commercially  speaking,  includes  a  number  of  hard, 
durable  rocks,  such  as  granite  proper,  syenite,  gneiss,  schist,  dio- 
rite,  and  andesite,  which  are  composed  of  silicates — usually  three 
or  more — and  principally  quartz,  the  feldspars  and  the  micas, 
pyroxene  and  amphibole.  It  is  used  in  enormous  quantities  in 
buildings,  in  paving  blocks  and  in  construction  of  bridges  and 
dams,  monumental  work,  flagstones  and  curbstones,  crushed  stone, 
etc. 

BASALT  and  the  related  rocks  include  basalt,  diabase  and  other 

*  The  facts  and  figures  are  taken  from  Mineral  Resources  of  the  U.  S.,  1914  and 

479 


480  MINER ALOG  Y. 

dark  igneous  rocks  similar  in  composition  and  properties.  Their 
uses  are  chiefly  as  crushed  stone  for  roads,  railroad  ballast  and 
concrete. 

SANDSTONE  is  composed  of  grains,  chiefly  quartz,  with  a  little 
feldspar,  mica  or  other  minerals,  and  is  classified  as  siliceous, 
ferruginous,  calcareous  or  argillaceous,  according  to  the  nature  of 
the  cement  which  binds  the  grains  together.  Its  uses  are  the  same 
as  those  of  granite,  but  a  larger  proportion  of  the  quantity  quarried 
is  used  in  building. 

BLUESTONE  is  a  very  hard,  durable,  fine-grained  sandstone, 
cemented  together  with  siliceous  material.  It  is  used  principally 
for  flag  and  curb  stone. 

SLATE  is  used  chiefly  as  roofing  material  and  for  interior  work, 
such  as  blackboards,  table  tops,  sinks,  etc.  Small  amounts  are 
ground  for  mineral  paint. 

The  production  of  silica  or  other  silicates  for  economic  purposes 
in  the  United  States  in  1915  was  valued  at  over  $31,000,000  and 
may  be  summed  up  as: 

Short  Tons.  Value. 

Quartz "2,575  #273,553 

Infusorial  earth  and  Tripoli 611,021 

Feldspars "3. 769  629,356 

Micas 4,236  428,769 

Garnets 4,3<>i  139-584 

Asbestos  (amphibole  and  serpentine) i,73i  76,952 

Talc  and  soapstone 186,891  1,891,582 

Clays*  (kaolinite,  etc.) 2,209,860  3-756,568 

Fuller's  earth  (kaolinite,  etc.) 47,901  489,219 

Sand  (chiefly  quartz)   95,46i  386,261 

Millstones,  Buhrstones,  grindstones 816,134 

Sand  and  gravel  for  building,  glass  making, 

molding,  paving,  grinding,  etc 76,603,303  23,121,617 

Individual  Minerals  or  Groups. 

QUARTZ  is  used  in  large  amounts  in  the  manufacture  of  sand- 
paper, porcelain,  pottery,  glass,  honestones,  oilstones,  and  as 
a  flux.  Other  large  uses  are  as  a  wood  filler  and  in  paints,  scouring 
soaps,  the  making  of  carborundum  and  ferro-silicon.  Fused 
quartz  is  used  for  chemical  apparatus,  and  colored  and  chalce- 
donic  varieties  are  used  as  semi-precious  or  ornamental  stones. 

*  1914.  Clay  products  in  1915  were  valued  at  $37,325,388  of  which  "white  ware 
products"  and  "sanitary  products"  represented  about  two  thirds. 


SILICA    AND    THE  ROCK-FORMING   SILICATES.        481 

INFUSORIAL  EARTH  and  TRIPOLI  are  calcined  and  made  into 
water  filters,  polishing  powders,  soap  filling  and  boiler  and  steam- 
pipe  covering. 

FELDSPAR  is  crushed  in  large  quantities  for  admixture  with 
kaolin  in  the  manufacture  of  porcelain  and  chinaware,  chiefly 
to  form  the  glaze,  but  partly  mixed  with  the  kaolin  and  quartz  in 
the  body  of  the  ware.  It  is  also  used  in  enamel  brick  and  tile, 
and  as  binder  for  emery  and  corundum  wheels.  The  purest  is 
used  in  the  manufacture  of  artificial  teeth. 

For  AMPHIBOLE  see  Serpentine. 

THE  MICAS,  especially  muscovite  and  phlogopite,  have  become 
of  great  importance  as  non-conductors  in  electrical  apparatus,  and 
are  also  used  in  stove  and  furnace  doors.  The  larger  sheets  are 
cut  and  split  to  the  desired  size;  the  waste  is,  to  some  extent, 
built  up  into  plates  suitable  for  certain  grades  of  electrical  work, 
and  for  covering  steam  boilers  and  pipes.  Large  amounts  of 
formerly  wasted  material  are  now  ground  and  used  for  decorative 
interior  work,  to  ornament  porcelain  and  glassware,  to  spangle  wall 
paper,  in  calico  printing,  as  a  lubricant  and  more  recently  as  an 
absorbent  of  nitro-glycerine  and  in  the  manufacture  of  certain 
smokeless  powders. 

BIOTITE  bronzed  by  heating  is  used  for  decorative  purposes 
and  lepidolite  in  glass  making. 

GARNET  is  ground  for  an  abrasive. 

SERPENTINE  is  to  some  extent  mined  and  used  as  ornamental 
stone,  but  is  commercially  classed  with  the  marbles.  The  fibrous 
varieties  of  both  amphibole  and  serpentine  are  known  commer- 
cially as  asbestos,  and  are  extensively  made  into  yarns,  ropes 
and  paper  for  fire-proof  purposes,  boiler  and  steam-pipe  cover- 
ing, piston  packing,  theatre  curtains,  firemen's  suits.  It  is  also 
used  for  fire-proof  paints  and  cements,  and  for  lining  safes. 
Asbestos  of  long  fine  fiber  is  used  in  the  laboratory  as  a  filtering 
medium. 

FIBROUS  TALC  and  compact  talc,  or  soapstone,  are  extensively 
used,  the  former  for  grinding  to  "mineral  pulp,"  used  in  paper 
manufacture,  the  latter  for  many  purposes,  usually  because  it  is 
refractory,  expands  and  contracts  very  little,  retains  heat  well  and 
is  not  attacked  by  acids.  These  properties  make  it  valuable  in 
32 


482  MINER  ALOG  Y. 

furnaces,  crucibles,  sinks,  baths,  hearths,  electrical  switch  boards 
and  cooking  utensils.  Talc  is  also  used  in  cosmetics,  refractory 
paints,  slate  pencils,  crayons,  gas  tips,  as  a  lubricant  and  in  soap 
making. 

CHLORITE  is  ground  and  us:d  in  hard  rubber,  rubber  tires, 
foundry  facings,  etc. 

KAOLINITE  AND  CLAY. — Enormous  and  varied  industries  use  as 
their  raw  material  the  beds  of  clay  which  result  from  the  decom- 
position of  the  feldspars  and  other  silicates.  These  beds  are 
composed  in  part  of  some  hydrous  aluminum  silicate  such  as  kaolin- 
ite,  but  usually  with  intermixed  quartz,  mica,  undecomposed 
feldspar,  oxides  and  sulphides  of  iron.  Their  properties  and  uses 
depend  chiefly  upon  their  composition. 

The  clay  industries  include  the  manufacture  of  common  brick, 
paving  brick,  fire-brick,  and  hydraulic  cement,  all  varieties  of 
earthenware,  stoneware  and  porcelain,  terra  cotta,  sewer  pipes  and 
drain  tiles,  and  are  carried  on  all  over  the  country  and  the  world. 

FULLERS  EARTH,  a  kind  of  clay,  is  used  in  the  refining  and 
clarifying  of  mineral  oils,  and  for  bleaching  lard  and  cottonseed  oils. 

THE  OTHER  SPECIES  AND  GROUPS  aside  from  a  limited  use  of 
transparent  or  brightly  colored  material  as  precious  or  ornamental 
stone  can  not  be  said  to  have  present  economic  importance. 

SILICA. 

The  minerals  described  are: 

Quartz  SiO2  Hexagonal 

Chalcedony  SiO2 

Tridymite  SiO2  Hexagonal 

Opal  Si02.wH2O 

Various  other  names  have  been  given,  some  based  on  optical 
differences  as  quartzine,  hissatite,  ps eudo chalcedony ,  lutecite,  some 
on  specific  gravity  as  granulina  and  jenzschite.  Of  them  all 
cristobaltite  is  best  characterized  and  apparently  represents  the 
form  which  silica  takes  if  formed  at  high  temperatures. 

FORMATION   AND    OCCURRENCE   OF   SILICA. 

According  to  experiments  silica  by  slowly  increasing  tempera- 
tures passes  through  the  various  conditions  of  a  quartz,  0  quartz, 
tridymite  and  cristobaltite. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.        483 

a  quartz  is  ordinary  quartz  like  that  of  mineral  veins  at  ordinary*  temperatures. 
If  heated  above  575°  C.  it  develops  the  characteristic  etch  figures  of  /3  quartz  (quartz 
of  the  granites  and  porphyries).  It  is  unstable  |  above  800°  CM  tending  to  pass  into 
tridymite  above  800°  C.  and  into  cristobaltite  at  1,470°. 

The  occurrences  may  be  grouped  as: 

Crystallization  from  Magma. 

Quartz  as  the  youngest  constituent  of  granites,  rhyolites  and 
quartz  porphyries  and  as  a  less  important  constituent  of  syenite 
and  some  basic  igneous  rocks. 

Tridymite  chiefly  in  volcanic  rocks  trachyte,  rhyolite,  and  ande- 
site. 

Pegmatites. 

Quartz  in  enormous  crystals.  Dakota,  Maine,  Connecticut, 
Norway,  etc. 

Veins. 

Quartz  both  as  chief  gangue  of  ore  veins  and  alone. 
Chalcedony,  opal  and  fine  grained  mixtures  as  later  constituents. 

Sediments. 

Mechanical  Sediments. — Quartz  as  chief  part  of  sand  and  sand- 
stone and  important  part  of  shale.  Tripoli  results  from  leaching 
out  of  calcareous  material  from  siliceous  limestone  as  in  S.  E. 
Missouri. 

Chemical  Sediments. — Opal,  chalcedony  and  sometimes  quartz 
by  hot  springs  and  from  the  colloidal  silica  formed  by  weathering. 

Sediments  due  to  Organisms. — Diatomaceous  Earth.  Microscopic 
water  plants,  called  diatoms,  build  silica  into  their  cells.  Their 
remains  accumulate  both  in  salt  and  fresh  water,  forming  beds. 
The  Richmond  beds  from  the  Chesapeake  to  Petersburg,  Virginia, 
are  in  parts  30  feet  thick.  The  Bilin,  Bohemia,  beds  are  14  feet 
thick.  Other  large  deposits  exist  near  Socorro,  New  Mexico 
and  Nevada. 

Metamorphic  Rocks. 

As  quartzite,  quartz  schist  and  an  essential  constituent  of  other 
rocks  partly  primary,  partly  secondary. 

*  Am.  Jour.  Sci.  48,  28,  293. 
t  Ibid.,  22,  276. 


484 


MINERALOGY. 


THE   OPTICAL   DETERMINATION   OF  THE   SILICAS. 


QUARTZ Uniaxial  +  1-553     1-544 

CHALCEDONY Biaxial    —         1-537 

TRIDYMITE Biaxial     +        1.47? 

OPAL Isotropic  1.446 


7  —  a 
0.009 


0.002 


In  Thin  Sections. 

Quartz. — Usually  fresh  unweathered  and  without  definite  shape. 
Low  relief,  smooth  surface.  Interference  colors  gray  or  first 
order  yellow.  Basal  sections  dark  between  crossed  nicols  and 
with  convergent  light  giving  uniaxial  cross  and  sometimes  one  ring 
red  on  outer  edge,  blue  on  inner.  Circularly  polarizing.  Basal 
sections  i  mm.  thickness  turn  the  plane  of  polarization  for  yellow 
light  21.7°  to  right  or  left. 

Chalcedony. — Between  crossed  nicols  radial  and  parallel  fibres, 
each  of  which  has  parallel  extinction,  and  negative  elongation.  If 
spherulitic  may  show  dark  cross. 

Tridymite. — Tile-like  aggregates  with  strong  relief  and  rough 
surface.  Hardly  noticeable  birefringence.  With  crossed  nicols 
and  convergent  light  distorted  biaxial  figure.  (Uniaxial  at 
130°  C.) 

Opal. — Shapeless  with  strong  relief,  rough  surface  and  dark 
between  crossed  nicols  or  may  show  double  refraction  and  even 
a  negative  cross  (hyalite)  as  result  of  strain. 

QUARTZ.— Rock  Crystal,  Amethyst. 

COMPOSITION. — SiO2,  (Si  46.7,  O  53.3  per  cent.). 
GENERAL  DESCRIPTION. — A  hard,  brittle  mineral  which  is  best 
known  in  transparent,  glassy,  hexagonal  crystals,  colorless,  and  as 


FIG.  470. 


FIG.  471. 


FIG.  472. 


SILICA    AND    THE  ROCK-FORMING   SILICATES. 


485 


the  somewhat  greasy  lustred,  shapeless,  transparent  mineral  of 
granite  and  other  igneous  rocks.  Colorless  if  pure,  but  often 
yellow,  violet,  or  smoky  and  more  rarely  other  colors. 

CRYSTALLIZATION. — Hexagonal.     Class   of   trigonal   trapezohe- 
dron,  p.   55.     Axis  c  =  1.0999.     Usually  a  combination  of  unit 


FIG.  473. 


FIG.  474- 


FIG.  475. 


FIG.  476. 


prism  m  with  one  or  both  unit  rhombohedra,  /  and  f,  the  former 
often  larger  and  brighter,  and  the  prism  faces  nearly  always  hori- 
zontally striated.  The  second  order  pyramid  s  =  (20,  :  2a  :  a  :  2c)  ; 
{1121};  frequently  occurs  and  rarely  the  trapezohedral  faces 
x  =  (|a  :  6a  :  a  :  6c),  {5161) ;  either  right,  Fig.  475,  or  left,  Fig. 
476.  Supplement  angles  pp  =  85°  46';  mp  =  38°  13';  ms  =  37° 
58';  mx  =  12°  i'. 

Twinned  crystals  are  not  rare.     See  page  68. 

Physical  Characters.     H.,  7.     Sp.  gr.,  2.65  to  2.66. 

LUSTRE,  vitreous  to  greasy.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle  to  tough. 

COLOR,  colorless  and  all  colors. 
CLEAVAGE,  difficult,  parallel  to  rhombohedron. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  With  soda,  fuses  with 
marked  effervescence  to  a  clear  or  opaque  bead,  according  to  the 
proportions  used.  Insoluble  in  salt  of  phosphorus  and  slowly 
soluble  in  borax.  Insoluble  in  all  acids  except  hydrofluoric. 

VARIETIES. 

Rock-forming  quartz  is  colorless  or  slightly  cloudy  or  rose 
tinted,  the  quartz  of  ore  veins  is  frequently  amethystine.  The 
principal  varieties,  which  are  discussed  more  at  length  under 
quartz  as  a  semi-precious  stone,  p.  567,  are 


486  MINER ALOG  Y. 

Rock  Crystat.-rPme,  colorless  or  nearly  colorless  quartz. 

Amethyst. — Purple  to  violet  and  shading  to  white.  Fracture 
shows  lines  like  those  of  the  palm  of  the  hand.  Color  disappears 
on  heating,  and  is  probably  due  to  a  little  manganese. 

Rose  Quartz. — Light-pink  or  rose-red,  becoming  paler  on  long 
exposure  to  light.     Usually   massive.     Colored  by  titanium   or. 
manganese. 

Yellow  Quartz  or  False  Topaz. — Light  yellow. 

Smoky  Quartz. — Dark  yellow  to  black.  Smoky  tint,  due  to 
some  carbon  compound. 

Milky  Quartz  or  Greasy  Quartz. — Translucent.  Usually  mass- 
ive. Common  as  a  rock  constituent. 

Ferruginous  Quartz. — Opaque,  brown  or  red  crystals,  sometimes 
small  and  cemented  like  a  sandstone. 

Aventurine. — Spangled  with  scales  of  mica,  hematite  or  goethite. 

Cat's  Rye. — Opalescent,  grayish-brown  or  green  quartz  with  in- 
cluded parallel  fibers  of  asbestus. 

REMARKS. — The  formation  of  quartz  is  discussed  on  p.  483,  and  its  uses,  p.  480. 
Localities  are  infinite  in  number,  a  few  famous  ones  being  Switzerland;  Japan; 
Carrara,  Italy;  Herkimer  Co.,  New  York;  Hot  Springs,  Arkansas;  Alexander  Co., 
North  Carolina. 

CHALCEDONY. 

COMPOSITION. — Silica  with  occasionally  a  little  water. 

GENERAL  DESCRIPTION. — Bluish  gray  or  translucent  material  in  mammillary 
linings  of  cavities  and  concretions.  Lustre  like  wax.  Grades  into  more  highly  colored 
and  more  opaque  varieties.  H.,  6.5  to  7.  Sp.  gr.,  2.62  to  2.64. 

CRYSTALLIZATION. — Never  in  crystals  visible  to  the  naked  eye  but  under  the  micro- 
scope with  crossed  nicols  is  seen  to  be  composed  of  minute  radiating  needle 
crystals. 

VARIETIES. — Optically  distinct  from  quartz.     The  color-names  such  as  Agate, 
Carnelian,  Sard,  Onyx,  Sardonyx,  Chrysoprase,  Bloodstone,  are  discussed  on  p.  572: 
Other  very  common  materials  are  essentially  chalcedony,  such  as 
Flint. — Smoky-gray   to  nearly  black,  translucent  nodules,  found  in  chalk-beds. 
Jasper. — Opaque    and      containing    considerable 
amounts  of  iron,  and  alumina,  and  often  highly  col- 
ored, as  red,  brown,  or  yellow. 

Touchstone. — Velvet-black  and  opaque,  on  which 
metal  streaks  are  easily  made  and  compared. 

TRIDYMITE. 
FIG.  477.  COMPOSITION. — SiOa. 

GENERAL  DESCRIPTION.— Small,  colorless,  hexag- 
onal plates.  Often  in  wedge  shaped  groups  of  two  or  three,  Fig.  477.  Usually 
prism  and  base  sometimes  pyramidal  faces  from  which  c  =  1.6304  calculated. 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        487 

PHYSICAL  CHARACTERS. — Transparent.  Lustre,  vitreous.  Color,  colorless  or 
white.  Streak,  white.  H.,  7.  Sp.  gr.,  2.28  to  2.33.  Brittle. 

BEFORE  BLOWPIPE,  ETC. — Like  quartz,  but  soluble  in  boiling  sodium  carbonate. 

OPAL. 

COMPOSITION. — SiO2.wH2O,  (H2O,  5  to  12  per  cent.). 

GENERAL  DESCRIPTION. — Colorless,  white  and  many  colored 
"veins"  and  incrustations  with  internal  color  reflections.  More 
often  without  ' '  opalescence "  but  translucent  and  with  wax-like 
to  porcelain-like  lustre.  Also  free  masses  of  rounded,  kidney, 
stalactitic  and  other  shapes  often  dull  or  pumice-like.  Color- 
less masses  like  drops  of  melted  glass  and  clay  like  or  chalky 
beds. 

CRYSTALLIZATION. — No  crystalline  structure  s  evident  and 
apparently  opal  is  "  amorphous"  in  the  most  complete 
sense. 

Physical  Characters.     H.,  5.5  to  6.5.     Sp.  gr.,  2.1  to  2.2. 

LUSTRE,  vitreous,  pearly,  dull.          TRANSPARENT  to  opaque. 
STREAK,  white.  TENACITY,  brittle. 

COLOR,  colorless  and  all  colors. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  Becomes  opaque  and 
yields  more  or  less  water.  Soluble  in  hydrofluoric  acid  more 
easily  than  quartz  and  soluble  in  caustic  alkalies^ 

VARIETIES. 

Precious  and  Fire  Opal. — With  play  of  colors. 

Common  or  Semi-Opal. — Translucent  to  opaque,  with  greasy 
lustre  and  of  all  colors,  but  without  play  of  colors. 

Hyalite. — Colorless  transparent  masses  resembling  drops  of 
melted  glass  or  of-  gum  arabic. 

Geyserite,  Siliceous  Sinter. — Loose,  porous  opal  silica  deposited 
from  hot  water.  Opaque,  brittle  and  often  in  stalactitic  or  other 
imitative  shapes.  Pearl  Sinter. — Pearly,  translucent  material 
found  in  volcanic  tufa  and  near  hot  springs  is  similar. 

Diatomaceous  or  Infusorial  Earth. — Massive,  chalk-like  or  clay- 
like  material  composed  of  the  remains  of  diatoms. 

Tripoli. — Residue  from  leached-out  siliceous  limestone. 

For  opal  as  a  precious  stone  see  p.  571. 


488  MINERALOGY. 

THE  FELDSPARS. 

The  feldspars  here  described  are : 

Orthoclase  KAlSi3O8  Monoclinic 

Microcline  KAlSi3O8  Triclinic 

Plagioclase  w(NaA!Si3O8)  +  «(CaAl2Si2O8)  Triclinic 

Albite,  oligoclase,  andesite,  labradorite,  bytownite  and  anorthite  are 
included  under  plagioclase  and  the  barium  feldspars  hyalophane 
and  celsian  are  briefly  mentioned  after  orthoclase. 

This  group  of  silicates  constituting  nearly  sixty  per  cent,  of  the 
crust  of  the  earth  is  believed  to  be  composed  of  three  fundamental 
substances,  KAlSi3O8,  NaAlSi3O8  and  CaAl2Si2O8.  The  isomorph- 
ous  mixtures  of  these  are  given  different  names,  but  they  all  have 
many  points  of  close  resemblance,  such  as  crystal  angles,  habit, 
modes  of  twinning,  cleavage  angles,  hardness  and  specific  gravity. 

FORMATION  AND   OCCURRENCE   OF   FELDSPARS. 
Their  occurrences  may  be  summarized  as  follows: 
Crystallization  from  Magma. 

Orthoclase. — Opaque  or  nearly  in  granite,  syenite,  porphyry  and 
more  glassy  in  trachyte,  phonolite,  rhyolite,  etc. 

Microcline. — In  granites. 

Albite. — Not  prominent  as  a  primary  mineral.  On  chemical 
grounds  considered  to  be  present  in  granites,  groundmass  of 
porphyry,  etc.,  and  acid  eruptives. 

Oligoclase  and  andesite. — More  common  in  granites  than 
albite.  Very  frequent  also  in  syenite,  diorite,  trachyte,  andesite, 
diabase,  etc. ;  and  particularly  accompanies  orthoclase. 

Labradorite  and  bytownite  are  especially  in  gabbros  and  norites 
but  also  in  other  basic  rocks,  diorite,  diabase,  basalt,  andesite,  etc. 

Anorthite. — In  gabbro  and  norite,  basalt,  etc.,  especially  if 
carrying  chrysolite.  Much  rarer  than  labradorite. 

Pegmatites. 

The  feldspars,  particularly  orthoclase,  microcline,    albite    and 
oligoclase,     are  the  principal  minerals  of  the  pegmatites. 
Contacts. 

Anorthite  occurs  as  a  contact  mineral  with  limestone  at  Mon- 
zoni,  Tyrol. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.        489 

Veins. 

Orthoclase. — The  variety  valencianite  (essentially  adularia),  oc- 
curs in  many  of  the  younger  ore  veins  evidently  deposited  from 
the  ascending  currents  and  often  replacing  former  gangue  min- 
erals.* Examples  are  Tonopah,  Nevada,  Gold  Road,  Arizona, 
Cripple  Creek,  Colorado;  Valencia,  Guanajuato. 

Sediments. 

The  arkose  sandstones  of  Portland,  Conn.,  are  high  in  feldspars 
and  they  are  abundant  as  fragments  and  in  shales  and  slates. 
The  potash  feldspars  predominate. 

In  Metamorphic  Rocks. 

The  plagioclases  are  less  abundant  than  orthoclase  and  micro- 
cline. 

The  potash  feldspar  is  usually  microcline.'f  Adularia,  however, 
occurs  in  clefts  in  the  crystalline  schists  as  in  the  Alps. 

Albite  is  common  in  gneiss  and  the  schists  (chlorite  schists  of 
Alps)  and  in  metamorphosed  eruptives. 

Labradorite  is  found  in  many  amphibolites. 

THE   OPTICAL    DETERMINATION    OF   FELDSPARS. 

If  the  mineral  is  a  feldspar  sections  in  balsam  will  show  frequent 
crystal  outlines,  low  relief  like  that  of  quartz,  gray  to  middle 

first  order  colors,  frequent  cleav- 

j  .    •      •        u-     •  i  FlG- 478> 

age  cracks  and  twinning,  biaxial 

interference  figures  and  very  of- 
ten cloudiness  from  weathering. 
Crushed  fragments  will  be  lath- 
like. 

If  orthoclase  twinning  will  be 
common  and  sections  showing  it 
will  be  divided  into  two  parts, 
Fig.  478,  which  extinguish  for  dif- 
ferent positions  between  crossed 
nicols  (Carlsbad  law)  or  the  divi- 
sion will  be  diagonal  with  the  two 
parts  exstinguishing  at  the  same  Sanidine,  Carlsbad  twin.  (Cohen.) 

*  Lindgren,  Mineral  Deposits,  434  to  438. 
f  Iddings,  "Rock  Minerals,"  237. 


490 


MINERALOGY. 


time  but  with  the  X  and  Z  directions  crossed  (Baveno  law) ;  the 
material  will  rarely  be  clear  and  pellucid. 

If  microdine  most  sections  will  show  between  crossed  nicols  the 
plaid  or  grating  structure  of  dark  and  light  bands  due  to  two 
systems  of  twinning,  as  shown  in  Fig.  479. 

FIG.  479- 


Microcline  grating  structure.     (Finlay.) 

\ 

If  plagiodase  there  will  usually  show  between  crossed  nicols 
parallel  dark  and  light  bands  due  to  multiple  twinning,  with  the 
lamellae  parallel  to  (oio)  the  brachy  pinacoid  (Albite  law),  which 
may  be  broad,  Fig.  480,  or  narrow,  Fig.  481,  or  both,  or  may 
pinch  out.  Sometimes  a  second  series  crosses  these  at  different 
angles  in  different  varieties  (Pericline  law) . 

The  More   Exact   Optical    Determination   in   Sections   of   Known  Orientation 
by  Extinction  Angles. 

On  account  of  the  two  easy  cleavages  (ooi)  and  (oio)  flakes  of 
known  orientation  are  easily  obtained  and  crushed  fragments  also 
tend  to  furnish  these  though  in  orthoclase  plates  parallel  (ooi) 
predominate  while  in  plagioclase  plates  parallel  (oio)  are  more 
common  because  of  the  lamellar  development  parallel  to  it. 

These  cleavage  sections  are  much  used,  the  " Guide"  or  reference 
line  in  each  being  the  trace  of  the  other  cleavage.  The  extinction 
angles  may  be  positive  or  negative,  the  rule  being  that  with  the 
sections  in  the  positions  of  Figs.  482  and  483,  with  the  cleavage 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        491 
FIG.  480.  FIG.  481. 


Plagioclase,  showing  broad  lamellae, 
in  gabbro.     (Cohen.) 


Plagioclase,  showing  narrow  lamellae, 
in  diabase.     (Cohen. ) 


cracks  parallel  to  a  cross  hair,  clockwise  rotations  are  +  (positive) 
and  counter  clockwise  are  —  (negative) . 


FIG.  482. 


FIG.  483. 


Feldspars. 
Section  (oio).  Section  (ooi). 

These  angles  together  with  other  constants  are  as  follows: 


Species 

Indices. 

Birefrin- 
gence. 

Extinction  Angles. 

Michel 
Levy. 

I     i     •• 

•y  —  a 

on  (coi) 

on  (oio) 

Orthoclase  
Microcline  

.526 
•529 
•540 
•545 
•557 
1-563 
1.588 

•519 
.522 
•532 
•537 
•  549 
•  555 
•  575 

O.OO7 
O.OO? 
O.008 
O.OO8 
0.008 
O.O08 
O.OI3 

0° 

+isi° 

+  4° 
+  2° 

-     ^° 

-    5° 
-37° 

+   5° 
+  5i° 
+  I9^° 
+   8° 
-    8° 
-18° 
-36° 

1  8° 
1  6° 
5° 
1  6° 

27° 

53° 

Albite  
Oligoclase  
Andesite  
Labradorite  
Anorthite  

492 


MINERALOGY. 


Extinctions  on  Sections  Perpendicular  to  (oio).  Michel  Levy 
Method. — In  rock  sections  (oio)  and  (ooi)  may  be  difficult  to  find 
but  any  section  perpendicular  to  a  twin  plane  will,  when  the  twin 
is  parallel  to  one  of  the  nicols,  be  equally  illuminated  and  the  angles 
of  extinction  with  this  line  will  be  equal.  But  there  are  many 
such  sections  giving  different  extinction  angles  and  only  the 
maximum  extinction  angles  are  characteristic.  Hence  numerous 
sections  must  be  tried  and  only  the  larger  angles  considered.  The 
maximum  extinction  angles  are  tabulated  above.  Fouque  deter- 
mined the  orientation  of  sections  by  convergent  light  tests  in 
sections  perpendicular  the  acute  or  obtuse  bisectrix. 

ORTHOCLASE.— Feldspar,  Potash  Feldspar. 

COMPOSITION. — KAlSi3O8,  with  some  replacement  by  Na. 

GENERAL  DESCRIPTION. — Cleavable  masses,  showing  angle  of  90; 
and  monoclinic  crystals,  of  flesh-red,  yellow  or  white  color.  Also 
compact,  non-cleavable  masses,  resembling  jasper  or  flint.  Some- 
times colorless  grains  or  crystals. 

CRYSTALLIZATION.  —  Monoclinic.  Axes  /?  =  63°  57';  a  :%:  c 
=  0.659  :  i  10.555.  Most  frequent  forms:  unit  prism  mt  pina- 
colds  b  and  c  and  positive  orthodomes  o  =  (a  :  oo  b  :  c);  J 101 } ; 
and  y  =  (a  :  oo  b  :  2c);  (201).  Supplement  angles  are  :  mm 
=  61°  13';  cm  =  67°  47';  co  =  50°  17';  cy  =  80°  18'. 


FIG.  484. 


FIG.  485. 


FIG.  486. 


FIG.  487. 


- 


Twin  forms  of  Carlsbad  type,  Fig.  488,  twin  plane  the  ortho- 
pinacoid,  are  very  common;  the  Baveno  type,  Fig.  489,  twin  plane 
a  clinodome,  and  Mannebacher  type,  twin  plane  the  base  c,  Fig. 
490,  are  less  common. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.        493 
FIG.  488.  FIG.  489.  FIG.  490. 


Physical  Characters.     H.,  6  to  6.5.  Sp.  gr.,  2.44  to  2.62. 
LUSTRE,  vitreous  or  pearly.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  flesh -red,  yellowish,  white,     CLEAVAGE,  parallel  to  c  and 
colorless,  gray,  green.  b,  hence  at  right  angles. 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  in  thin  splinters  to  a  semi- 
transparent  glass  and  colors  the  flame  violet.  Insoluble  in  acids. 
VARIETIES. 

Ordinary.  —  Simple  or  twinned  crystals,  sometimes  of  great  size, 
of  nearly  opaque  pale  red,  pale  yellow,  white  or  green  color. 
More  frequently  imperfectly  formed  crystals  and  cleavable  masses, 
in  the  granitic  rocks. 

Adularia.  —  Colorless  to  white,  transparent,  often  opalescent. 
Usually  in  crystals. 

Sanidine  and  Rhyacolite.  —  Glassy,  white  or  colorless  crystals  in 
lava,  trachyte,  etc. 

Loxoclase.  —  Grayish-white  or  yellowish  crystals,  which  have  a 
tendency  to  cleave  parallel  to  the  ortho  pinacoid. 

Felsite.  —  Jaspery  or  flint-like  masses  of  red  or  brown  color. 

SIMILAR  SPECIES.  —  Differs  from  the  other  feldspars  in  the  cleav- 
age at  90°,  the  greater  difficulty  of  fusion,  the  absence  of  stria- 
tions.  The  very  common  red  or  brownish  color  of  orthoclase 
does  not  occur  in  plagioclase. 

REMARKS. — The  occurrence  and  uses  are  described  on  p.  488,  and  481.  It  changes 
to  kaolin  quartz,  opal,  epidote  and  sericite,  by  the  removal  of  bases  through  the  action 
of  acid  waters.  Orthoclase  is  quarried  at  South  Glastonbury  and  Middletown, 
Conn.;  Edgecomb  and  Brunswick,  Me.;  Chester,  Mass.;  Brandywine  Summit,  Pa.; 
Tarrytown  and  Fort  Ann,  N.  Y.,  and  the  Spruce  Pine  district,  N.  C. 

HYALOPHANE.      (K2,  Ba)Al2(SiO3)4  and  CELSIAN.      BaAhSizOs,  are  barium 


494  MINER  ALOG  Y. 

feldspars,  stated  by  Iddings  to  be  "monoclinic  in  all  discernible  physical  properties." 
The  former  resembles  adularia  and  occurs  in  dolomite  in  Binnenthal,  Switzerland, 
and  Jakobsberg,  Sweden.  The  latter  is  massive  cleavable  from  Jakobsberg,  Sweden. 

MICROCLINE. 

COMPOSITION. — KAlSi3Os 

GENERAL  DESCRIPTION. — Like  orthoclase.  There  is  no  practicable  macroscopic 
distinction  between  orthoclase  and  microcline  and  it  is  very  probable  that  they 
are  identical. 

One  theory  is  that  the  individuals  are  triclinic  and  submicroscopic,  but  that  in 
orthoclase  they  alternate  in  twin  position,  remaining  invisible  and  giving  an  "ap- 
parent monoclinic"  structure,  whereas  in  microcline  a  number  of  successive  indi- 
viduals are  parallel  followed  by  a  number  in  twin  position,  thereby  becoming  visible 
as  twin  lamellse,  but  grading  into  submicroscopic  and  apparently  monoclinic  portions. 

REMARKS. —  The  distinctions  are  optical  (see  p.  491  and  Fig.  479). 

PLAGIOCLASE. — Albite,  Anorthite,  and  Isomorphous  Mixtures. 

The  name  "  plagioclase"  was  originally  given  to  minerals  closely 
resembling  common  feldspar  in  cleavage,  crystal  form,  mode  of 
occurrence,  hardness,  specific  gravity  and  other  physical  charac- 
ters, but  with  the  angle  between  the  two  cleavages  about  86°  in- 
stead of  90°.  The  very  great  variations  in  composition  led  to  the 
establishment  of  several  species,  in  which,  however,  the  variations 
in  composition  were  still  great,  and  finally  to  a  theory,  now  gen- 
erally accepted,  which  may  be  expressed  as  follows  :  The  plagio- 
clases  consist  of  isomorphous  mixtures  of  two  (or  three)  triclinic  com- 
pounds, NaAlSizO&  and  CaAS2St208  (and  KAlSi^O^.  Some 
specimens  approach  the  end  members,  and  are  then  called  respec- 
tively albite,  anorthite  (and  microcline),  but,  in  general,  distinct  species 
cannot  be  said  to  ezist. 

In  accordance  with  this,  the  more  prominent  species  names  are 
here  given  as  varieties  of  the  group  name  PLAGIOCLASE. 

COMPOSITION.  —  ?^(NaAlSi3O8)  +  ^(CaAl2Si2O8),  with  some  re- 
placement by  KAlSi3O8. 

GENERAL  DESCRIPTION.  —  Granular  masses  or  small  triclinic 
crystals,  or  coarser  masses.  Each  grain  or  crystal  cleaves  easily 
in  two  directions,  which  make  an  angle  of  about  86°  with  each 
other,  and  shows  on  one  or  both  surfaces  by  reflected  light  the 
parallel  "twin  striations."  Some  varieties  show  marked  play 
of  colors,  others  the  moonstone  effect.  Usually  light  colored, 
and  most  frequently  colorless,  white  or  faintly  tinged,  sometimes 
(labradorite)  dark  gray.  Just  about  the  hardness  of  a  good  knife. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         495 


CRYSTALLIZATION.  —  Triclinic,  usually  in  crystals  resembling  that 
shown  in  Fig.  491,  with  supplement  angles  mM  approximately 
60°,  and  frequently  twinned  either  by  the  albite  law,  twin  plane 
b,  Fig.  494,  which,  if  repeated,  results  in  striations  on  c;  or  by  the 
pericline  law,  twin  axis  the  macro  axis,  Fig.  493,  producing  stri- 
ations on  b. 

Albite  and  anorthite  are  frequently  crystallized,  the  other  varie- 
ties less  frequently. 


FIG.  491. 


FIG.  492. 


FIG.  493. 


— ; 


COMPOSITION  AND  SPECIFIC  GRAVITY  OF  TYPES. — Denoting 
NaAlSI3O8  by  Ab  and  CaAl2Si2O8  by  An  the  names  most  used 
are  as  follows: 

ALBITE  AbiAn0     to     Ab6Ani 

OLIGOCLASE  Ab6Ani    to    Ab3Ani 

ANDESINE  Ab3Ani     to    AbiAni 

LABRADORITE  AbiAni    to    AbiAn3 

BYTOWNITE  AbiAn3     to    AbiAn6 

ANORTHITE  AbiAn6    to 


The  percentage  composition  and  specific  gravities  of  types  are: 


Sp.  Gr.* 

SiO2. 

A1203. 

Na2O. 

CaO. 

AbiAno 

2.605 

68.7 

19.5 

II.  8 

o 

AbeAni  . 

64.9 

22.1 

IO.O 

3 

AbsAni  

2.649 

62.0 

24.O 

8.7 

5-3 

AbiAm  

2.679 

55-6 

28.3 

5-7 

10.4 

AbiAns  

49.3 

32.6 

2.8 

15.3 

AbiAne 

46.6 

34-1 

1.6 

17.4 

AboAni  

2.765 

43-2 

36.7 

0 

20.  i 

*  On  pure  artificial  feldspars  also  Ab2Am  2.660,  AbiAn2  2.710,  AbiAm  2.733. 
Natural  material  is  impure  and  ranges  2.5  to  2.8. 


496  MINERALOGY. 

Physical  Characters.     H.,  5  te  7-     Sp.  gr..  2.5-2.8  in  minerals. 

LUSTRE,  vitreous  or  pearly.  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  varies.  CLEAVAGES,  at  86°  approx. 

Distinguishing  the  Varieties. 

Something  can  be  judged  by  the  occurrence,  p.  488.  The  end 
members,  albite  and  anorthite,  are  less  common  than  the  others 
and  the  albite  and  oligoclase  or  andesine  are  to  be  expected  in  the 
more  acid  igneous  rocks  such  as  the  granites,  while  the  labradorite, 
bytownite  and  anorthite  favor  the  dark-colored  basic  rocks.  In 
the  schists  and  metamorphic  rocks  generally  albite  is  common. 

The  optical  distinctions  as  outlined  on  p.  490  are  conclusive 
if  the  orientation  is  known. 

A  few  simple  macroscopic  indications  are  as  follows: 

Albite. — Usually  pure  white,  granular  or  with  curved  cleavage 
surfaces,  or  in  crystals  (Figs.  491  to  493)  in  cavities.  Often 
encloses  the  rarer  minerals,  tourmaline,  beryl,  chrysoberyl,  topaz, 
etc.  Not  easily  altered. 

American  localities  are  Branchville,  Conn.;  Paris,  Maine;  Chesterfield,  Mass.; 
Amelia  Co.,  Virginia;  Pikes  Peak,  Colorado. 

Oligoclase  often  accompanies  orthoclase  as  grayish  white, 
translucent  masses,  with  somewhat  greasy  lustre  and  marked  twin 
striations.  Occurs  also  as  reddish  cleavable  masses,  sunstone, 
and  rarely  as  crystals. 

American  localities  are  Fine  and  McComb,  New  York;  Mineral  Hill,  Perm.; 
Bakersville,  N.  C. 

Andesine  is  similar  to  oligoclase. 

Observed  in  the  granular  and  volcanic  rocks  of  the  Andes.  Also  common  in  the 
Rocky  Mts.,  Sandford,  Maine,  etc. 

Labradorite  is  usually  in  dark  gray  cleavable  masses  often 
associated  with  hypersthene.  Commonly  iridescent,  showing 
beautiful  changing  colors,  blue,  green  and  red,  from  inclusions  of 
diallage,  ilmenite  or  goethite.  Striated  like  oligoclase.  Is  notably 
absent  in  localities  containing  orthoclase  and  quartz. 

Found  abundantly  in  the  Adirondacks,  N.  Y.,  in  the  Wichita  Mountains,  Ark., 
in  Quebec  and  in  Labrador. 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        497 

Bytownite,  originally  a  greenish  white  feldspar  from  By  town, 
Canada,  is  now  simply  a  name  for  plagioclase  between  labradorite 
and  anorthite. 

Anorthite. — Comparatively  rare  as  a  pure  mineral. 

Best  known  in  the  small  glassy  crystals  of  Vesuvius  and  the  white  crystals  of 
Miyake,  Japan,  often  covered  with  a  black  crust,  the  massive  granular  indianite  from 
India,  and  the  contact  mineral  of  Monzoni,  Tyrol. 

THE   FELDSPATHOIDS. 

The  minerals  described  are : 

Leucite  K.Al(SiO3)2  Isometric 

Melilitc  Cai2Al4(SiO4)2  Tetragonal 

Nephelite  7NaAlSiO4  +  NaAl(SiO3)2  Hexagonal 

Sodalite  Group  Isometric 

The  analcite,  p.  531,  of  certain  plutonic  rocks  near  Butte, 
Montana,  and  Pikes  Peak,  Colorado,  and  the  dike  at  Heron  Bay, 
L.  S.,  also  belongs  here. 

FORMATION   AND    OCCURRENCE   OF   FELDSPATHOIDS. 

Feldspathoids  are*  "  Silicates  of  alumina  and  an  alkali  or  alkaline 
earth  that  are  practically  equivalent  to  feldspars  in  their  relation 
to  rocks." 

They  form  from  magmas  unusually  rich  in  sodium  or  potassium 
and  are  limited  to  igneous  rocks  or  rarely  to  schists  resulting  from 
metamorphosis  of  igneous  rocks. 

Two  divisions  may  be  made. 

In  Volcanic  Rocks. 

Leucite. — Almost  entirely  confined  to  younger  eruptive  rocks, 
phonolite,  tephrite  and  other  leucite  rocks  and  their  tuffs. 

Melilite. — Restricted  to  younger  basic  eruptives,  such  as  augite 
bearing  basalts. 

Nephelite. — In  glassy  crystals  in  volcanic  ejecta,  phonolite- 
tephrite,  etc. 

Noselite  and  Haiiynite. — Almost  limited  to  microscopic  material 
in  phonolite,  etc.,  and  always  associated  with  nephelite  or  leucite, 

Sodalite. — In  microscopic  crystals,  trachytes,  phonolites  and 
lava. 

*  Kemp,  "Handbook  of  Rocks,"  p.  186. 
33 


498  MINERAL  OGY. 

In  Plutonic  Rocks. 

Leucite  rare  but  often  represented  by  pseudomorphs. 
Nephelite  as  massive  and  coarsely  crystalline  elaeolite  in  elseolite- 
syenite. 

Sodalite  common  in  elaeolite-syenite. 

OPTICAL    DETERMINATION    OF    FELDSPATHOIDS. 

7  a  7  —  a 

Leucite .' Biaxial      +  1.5809         1.5808  o.ooi 

Melilite Uniaxial  ±  1.631  1.629  0.002 

Nephelite Uniaxial  —  1.542  1.538  0.004 

Sodalite Isotropic  1.483 

Haiiynite  1 

Noselite    I IS°tr°plC  "^ 

In  Thin  Sections. 

Leucite. — Nearly  round  cross  sections.  Isotropic  in  small  crys- 
tals but  showing  intersecting  twin  lamellae  and  zonal  inclusions 
in  larger  crystals.  No  relief,  smooth  surface.  Low  bluish-gray 
interference  colors  best  proved  with  gypsum  red  test  plate. 

Melilite. — Lath-shaped  sections  or  irregular  often  with  markings 
parallel  the  length.  Marked  relief.  Very  low  interference  colors 
or  abnormal,  p.  138. 

Nephelite. — Rectangular  or  hexagonal  sections  in  volcanic  rock 
shapeless  in  plutonic.  No  relief,  smooth  surface,  low  first  order 
interference  colors.  Basal  sections  give  broad  cross,  no  rings. 
Other  sections  extinguish  parallel  cleavages. 

Hauynite,  Noselite,  Sodalite. — Dodecahedral  crystals  or  shape- 
less. Surface  rather  rough.  Gas  and  glass  inclusions  especially 
near  border.  Dark  between  crossed  nicols  or  abnormal.  Distinc- 
tions by  microchemical  tests. 

LEUCITE. 

COMPOSITION.— KA1(SIO3)2.  FlG-  494. 

GENERAL  DESCRIPTION. — Gray,  translucent  to 
white  and  opaque,  disseminated  grains  and  trap- 
ezohedral  crystals -in  volcanic  rock. 

CRYSTALLIZATION. — Isometric  externally,  but 
with  polarized  light,  showing  double  refraction 
at  all  temperatures  below  500°  C. 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        499 

Physical  Characters.     H.,  5.5  to  6.     Sp.  gr.,  2.45  to  2.50. 
LUSTRE,  vitreous  to  greasy,  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white  or  gray,  or  with  yellowish  or  red  tint. 

BEFORE  BLOWPIPE,  ETC.  Infusible.  With  cobalt  solution,  be- 
comes blue.  Soluble  in  hydrochloric  acid,  leaving  a  fine  powder 
of  silica. 

REMARKS. — It  is  not  common  in  America,  but  is  found  in  the  Leucite  Hills. 
Wyoming,  and  also  in  the  northwestern  part  of  the  same  state,  and  in  Montana, 
It  is  represented  by  pseudomorphs  at  Magnet  Cove,  Arkansas.  Very  common  in 
the  Vesuvian  lavas  and  in  other  parts  of  Italy. 

MELILITE. — Cai2Al4(SiO4)2  with  Na,  Mg  and  Fe  replacing  Ca  and  Al,  occurs  in 
short  prisms  and  in  tabular  tetragonal  crystals.  Color,  honey-yellow  to  brown. 
H.,  5.  Sp.  gr.,  2.9.  Fuses  quite  easily  to  a  yellowish  or  green  glassy  globule. 
Gelatinizes  with  hydrochloric  acid. 

It  is  found  in  the  Vesuvian  lavas,  certain  basalts  of  Wiirttemberg  and  the  Sandwich 
Islands  and  elsewhere. 

NEPHELITE.— Elseolite. 

COMPOSITION.— ;NaAlSiO4  +  NaAl(SiO3)2.  With  partial  re- 
placement of  Na  by  K  or  Ca. 

GENERAL  DESCRIPTION. — Small,  glassy,  white  or  colorless  grains 
or  hexagonal  prisms  with  nearly  flat  ends,  in  lavas  and  eruptive 
rocks,  or  translucent  reddish-brown  or  greenish  masses  and  coarse 
crystals,  with  peculiar  greasy  lustre. 

Physical  Characters.    H.,  5.5  to  6.     Sp.  gr.,  2.55  to  2.65. 
LUSTRE,  vitreous  or  greasy.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  colorless,  reddish,  brownish,  greenish  or  gray. 
CLEAVAGE,  prismatic  and  basal. 

BEFORE  BLOWPIPE,  ETC. — Fuses  to  a  colorless  glass.  When 
heated  with  cobalt  solution,  becomes  blue.  Soluble  in  hydro- 
chloric acid,  with  residue  of  gelatinous  silica. 

VARIETIES. — The  usually  massive  varieties,  with  greasy  lustre, 
are  called  elaeolite. 

REMARKS. — Southern  Norway;  Greenland;  Miask,  Urals;  Austin,  Texas;  Litch- 
field,  Me.;  Salem,  Mass.;  the  Ozark  Mountains,  Arkansas;  Cripple  Creek,  Col. 
are  important  localities  of  elaeolite.  Nephelite  is  abundant  in  the  lavas  of  Vesuvius, 
and  in  basalts  near  Heidelberg,  Germany,  and  Aussig,  Bohemia. 


500 


MINERALOGY. 


THE    SODALITE    GROUP. 

A  group  of  silicates  containing  the  unusual  radicals  Cl,  SO3  and  S.  The  formulae 
as  written  and  the  isometric  crystallization  suggest  a  relationship  to  garnet. 

SODALITE.— Na4(AlCl)Al2(SiO4)3  Is  found  in  bright  blue  to  gray  masses,  em- 
bedded grains,  concentric  nodules  resembling  chalcedony  and  rarely  dodecahedral 
crystals  sometimes  of  a  pale  pink  color.  It  occurs  at  Litchfield,  Me.,  various 
localities  in  Montana,  Quebec,  and  Ontario;  also  in  Vesuvius  lavas,  at  Kaiserstuhl, 
Baden;  and  Miask,  Urals. 

HAUYNITE.— 2(Na2Ca)Al2(SiO4)2.(Na2.Ca)SO4  possibly,  but  very  complex  and 
with  varying  proportions  of  Na  and  Ca.  Occurs  as  glassy  blue  to  green  imbedded 
grains,  or  rounded  isometric  crystals  in  igneous  rock. 

NOSELITE. — Na4(NaSO4.Al)Al2(SiO4)3  not  distinguishable  from  haiiynite  except 
by  microchemical  tests.* 

Haiiynite  is  from  Mt.  Dore,  Puy  de  Dome;  Vesuvian  lavas,  the  Eifel  and  Crazy 
Mt.,  Montana. 

Noselite  is  from  Lake  Laach,  Cape  Verde  Islands,  etc. 

THE  PYROXENE  AND   AMPHIBOLE   GROUPS. 

THE   PYROXENE    GROUP. 

Enstatite  (Mg.Fe)SiO3  Orthorhombic 

Hyperslhene  (Mg.Fe)SiO3  Orthorhombic 

Pyroxene  RSiO3  Monoclinic 

Acmite  NaFe(SiO3)2  Monoclinic 

Wollastonite  CaSiO3  Monoclinic 

Other  described  species  belonging  to  this  group  are  spodumene, 
rhodonite,  and  jadeite! 

THE  AMPHIBOLE   GROUP. 

The  minerals  described  are: 

Anthophyllite  (Mg.Fe)SiOs  Orthorhombic 

Amphibole  RSiO3  Monoclinic 

Glaucophane  NaAl(SiO3)2(Fe.Mg)SiO3  Monoclinic 

Crocidolite  NaFe  (SiO3)2FeSiO3 

The  compositions  of  the  two  groups  are  related,  but  while  the 
amphiboles  are  largely  formed  from  the  pyroxenesf  corresponding 
members  are  lower  in  calcium  and  higher  in  magnesium.  There 

*For  instance  gypsum  crystals  obtained  by  evaporating  the  hydrochloric  acid 
solution  prove  haiiynite. 

f  When  the  amphibole  retains  the  outward  form  of  the  pyroxene  it  is  called  uralite. 
The  change  usually  commences  on  the  surface  and  the  uralite  does  not  form  a  single 
compact  crystal,  but  consists  of  numerous  slender  columns  parallel  to  one  another. 
These  little  columns  or  fibers  have  their  I  and  5  axes  parallel  to  the  positions  of  these 
axes  in  the  parent  mineral. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         501 

are  also  close  relations  in  crystalline  form,  as  shown  by  the  follow- 
ing comparison  of  constants: 

Pyroxene  a  :  b  :  c     =  1.0921  :  I  :  0.5893     0  =  74°  10' 

Amphibole  a  :  %b  :  c  =  1.1022  :  I  :  0.5875     0  =  73°  58' 

The  "habit"  and  cleavage  are  however  always  different. 

FORMATION   AND    OCCURRENCE    OF    PYROXENES   AND   AMPHIBOLES. 

The  occurrences  may  be  classed  as 
Separations  from  Magma  in  Plutonic  Rocks. 

PYROXENES. 

Diopside,  and  some  augites  in  granites,  syenites  and  diorites. 
Enstatite,  hypersthene,  diopside,  diallage  and  darker  augites;  in 
more  basic  rocks,  gabbros,  norites,  pyroxenites,  peridotites,  etc. 
Acmite  in  nephelin  syenites,  granites,  etc. 

AMPHIBOLES. 

Common  hornblende  in  granite,  syenite,  diorite,  gabbro. 
Basaltic  hornblende  in  gabbro. 

Separations  from  Magma  in  Volcanic  Rocks. 

PYROXENES. 

Augite  as  important  constituent  of  many  volcanic  rocks,  espe- 
cially basalt,  melaphyre,  diabase,  andesite,  porphyries,  and  ash 
and  tuff  of  volcanoes. 

Enstatite  and  hypersthene  as  accessories  in  small  crystals. 

Acmite  in  leucite  and  nephelite  rocks. 

Diopside  and  sahlite  rare.     No  diallage. 


AMPHIBOLES. 

Basaltic  hornblende  chiefly  in  basalts,  andesites,  and  volcanic 
tuffs. 

Secondary  Crystallizations  in  Igneous  Rocks. 

The  amphibole  actinolite  is  common,  sometimes  formed  from 
pyroxene,  sometimes  from  hornblende.  Secondary  pyroxene  is 
rare. 

Contacts. 

The  PYROXENES,  fassaite,  wollastonite,  diopside,  sahlite  and  some- 
times augite  and  the  AMPHIBOLES,  edenite,  and  common  hornblende. 


502 


MINERALOGY. 


In  Metamorphic  Rocks. 

PYROXENES. 

Diopside  and  sahlite  in  clefts  in  the  schists  or  in  granular  lime- 
stone. 

Augite  less  frequent. 

Enstatite  and  hypersthene  in  metamorphosed  igneous  rocks, 
serpentine  and  some  gneiss. 

AMPHIBOLES. 

Tremolite  always  metamorphic,  especially  in  granular  limestone 
and  dolomite  in  regions  of  crystalline  schists. 

Actinolite  is  more  widespread,  not  only  as  a  secondary  mineral 
in  igneous  rocks  resulting  from  the  alteration  of  pyroxene  but 
forming  actinolite  schists  with  chlorite  and  epidote  or  magnetite 
and  as  crystallizations  in  talc. 

Hornblende  is  common,  sometimes  forming  hornblende  schist 
and  hornblende  gneiss. 

Anthophyllile  and  glaucophane  occur  in  schists,  the  former  often 
with  hornblende  or  actinolite,  the  latter  sometimes  forming  inde- 
pendent glaucophane  schists. 

OPTICAL   DETERMINATION    OF   PYROXENES   AND   AMPHIBOLES. 

The  characters  of  use  in  distinction  are: 


Refractive 
Indices. 

Birefrin- 
gence. 

Extinct. 

Pleochroism. 

y 

a 

7  —  a 

On  oio. 

PYROXENES: 

Enstatite 

1.669 
1-705 
1.702 
to 

1.727 
1.722 
1.813 

1.635 

.657 
.636 
.636 

.653 
639 

1.665 
1.692 
1.680 
to 
1.706 

1.697 
1.763 

1.621 

1.633 

1.609 
1.611 
1.629 
1.621 

O.O09 
0.013 
O.O22 

to 

O.O2I 
0.025 
0.050 

O.OI4 

O.O24 
O.027 
O.O25 
O.024 
O-OI8 

0° 
0° 

38°  to  45° 

38°  to  54° 
2°  to  5° 

35° 

0° 

16° 

15° 
15°  to  25° 
4°  to  6° 

Weak 
Strong,  red  to  green 

None 

Not  intense 
Strong,  yellow  to  green  or 
brown 
None 

Sometimes 
None 
Weak 
Strong  yellow  to  green 
Strong  blue  to  yellow 

Hypersthene  

Diopside  

Augite 

Acmite          .  . 

Wollastonite   

AMPHIBOLES: 

Anthophyllite  
Tremolite 

Actinolite  
Hornblende*  
Glaucophane  

The  indices  indicate  marked  relief  and  rough  surfaces  in  balsam.     Interference 
colors  in  thin  sections  (due  to  7  —  a)  will  be  rather  low  in  enstatite,  hypersthene 


SILICA   AND    THE  ROCK-FORMING  SILICATES. 


503 


and  wollastonite.  The  other  pyroxenes  will  show  very  bright  colors,  more  so  than 
the  amphiboles  because  of  the  strong  absorption  of  the  latter  in  direction  of  cleavage 
lines  of  longitudinal  sections. 

In  convergent  light.     All  are  biaxial  with  axial  plane  (oio). 


Pyroxenes: 

Axial  angle.  Sign. 

Enstatite ...  Large  + 

Hypersthene Large  — 

Pyroxene Large  + 

Acmite   Small  — 

Wollastonite Large  —  or  + 

Amphiboles : 

Anthophyllite Large  + 

Amphibole Large  — 

Glaucophane Medium  — 


Acute  bisectrix. 
\\c 
II  a 
—  36°  to  54°  to  c  (front) 

nearly  ||  c 
+32°  to  c  (back) 


—  70°  to  90°  to  c  front 

—  84°  to  86°  to  c  front 


Basal  sections  show  characteristically  different  outlines  and  cleavage  lines  in 
pyroxene,  Fig.  495,  and  in  amphibole,  Fig.  496.  They  yield  symmetrical  interference 
figures,  Fig.  266,  with  enstatite,  hype*sthene  and  anthophyllite,  and  may  show  the 
emergence  of  an  optic  axis,  Fig.  269,  with  the  other  pyroxenes  and  glaucophane. 


FIG.  495. 


FIG.  496. 


Pyroxene. 


Amphibole. 


The  section  (oio)  yields  the  most  characteristic  tests,  giving 
maximum  birefringence  (interference  colors)  pleochroism  and  ex- 
tinction angles.  It  is  parallel  to  the  axial  plane  therefore  may 
give  the  interference  figure  of  Fig.  267. 

In  finding  (oio)  in  a  rock  section  a  partial  guide  is  the  one  system  of  parallel 
cleavage  lines  (so  also  on  100)  and  these  maximum  interference  colors  and  pleochroic 
differences. 

The   extinction   angle   results  when   the   longitudinal   section, 


*  In  basaltic  hornblende  the  indices  are  higher  and  birefringence  so  high  that  no 
bright  colors  result  and  the  extinction  varies  from  o°  to  +  10°. 


Figs.  497, 498, 499, 

to  the  nearest  extinction. 


MINERALOGY. 
is  revolved  from  the  cleavage  lines  as  a  reference 

irrinn . 


This  direction  will  be  X  in  acmite,  and  wollastonite  and  Z  in  the  < 
may  be  proved  by  test,  p.  134,  for  faster  and  slower  ray  (elongation). 


wollastonite  and  Z  in  the  others  and  this 

nH  slnwpr  rav   fplnnpaHnTO 


Enstatite-Hypersthene.         Pyroxene  (Diopside).          Amphibole  (Tremolite). 

THE   ORTHORHOMBIC   PYROXENES. 

Enstatite  and  Hypersthene. 

Natural  iron  free  MgSiO3  is  not  known. 

COMPOSITION. — (Mg.Fe)SiO3.  Although  these  two  substances 
have  the  same  general  formula  and  nearly  identical  axial  ratios, 
the  increase  in  iron  contents  not  only  affects  such  characters  as 
color  fusibility,  and  specific  gravity  but  the  position  of  the  optic 
axes  so  that  Des  Cloizeaux  made  the  distinction,*  on  the  basis 
of  the  fact  that  with  about  10  per  cent.  FeO  the  optic  axial  angle 
was  90°,  between 

Enstatite  with  FeO  <  10  per  cent,  and  optically  +. 
Hypersthene  with  FeO  >  10  per  cent,  and  optically  — . 

EN  STATITE.— Bronzite. 

COMPOSITION.— (Mg.Fe)  SiO3. 

GENERAL  DESCRIPTION.— Brown  to  gray  or  green,  lamellar  or  fibrous  masses,  with 
sometimes  a  peculiar  metalloidal  lustre  (bronzite).  Rarely  in  columnar  orthorhombic 
crystals. 

PHYSICAL  CHARACTERS. — Translucent  to  opaque.  Lustre,  pearly,  silky  or  metal- 
loidal. Color,  brown,  green,  gray,  yellow.  Streak,  white.  H.,  5.5.  Sp.  gr.,  3.1  to  3.3. 
Brittle. 

BEFORE  BLOWPIPE,  ETC.— Fusible  on  the  edges.  Almost  insoluble  in  acids.  With 
cobalt  solution  is  turned  pink. 

*As  Dana  states  it,  "The  essential  difference  between  them,  according  to  Des- 
Cloizeaux,  lies  in  the  axial  dispersion  which  is  uniformly  p  <v  for  enstatite,  and 
p  >  v  for  hypersthene." 


SILICA   AND    THE  ROCK-FORMING   SILICATES. 


505 


REMARKS. — Occurrences  as  stated  on  p.  501 ;  also  found  in  meteorites.  The  largest 
crystals  (pseudomorphs)  are  from  the  apatite-iron  deposits  of  Bamle,  Norway.  The 
fibrous  talc  of  Edwards,  N.  Y.,  is  altered  enstatite.  Other  localities  are  Kupferberg, 
Bavaria,  and  Baste,  Harz. 

HYPERSTHENE. 

COMPOSITION. — (Mg.Fe)SiOs,  with  more  iron  than  enstatite 

GENERAL  DESCRIPTION. — Dark-green  to  black,  foliated  masses  or  rare  orthorhom- 
bic  crystals,  which  grade  into  enstatite.  Frequently  shows  a  peculiar  iridescence,  due 
to  minute  interspersed  crystals. 

PHYSICAL  CHARACTERS. — Translucent  to  opaque.  Lustre,  pearly  or  metalloidal. 
Color,  dark-green  to  black.  Streak,  gray.  H.,  5  to  6  Sp.  gr.,  3.4  to  3.5.  Brittle 

BEFORE  BLOWPIPE,  ETC. — Fuses  on  coal  to  a  black,  magnetic  mass.  Partially 
soluble  in  hydrochloric  acid. 

REMARKS. — It  occurs  at  St.  Paul,  Labrador,  and  the  Saranac  Region,  N.  Y.; 
with  labradorite;  Bodenmais,  Bavaria,  in  the  intrusive  pyrite  deposit;  Aranyer 
Berg,  Hungary;  Mt.  Dore,  Auvergne;  etc. 

BASTITE. — An  alteration  product  of  enstatite  near  serpentine  in  composition. 
It  is  usually  foliated  and  of  a  yellowish  or  greenish  color  and  has  a  peculiar  bronze-like 
lustre  on  the  cleavage  surface.  H.,  3.5-4.  Sp.  gr.,  2.5-2.7. 

PYROXENE.  —  Augite. 

COMPOSITION. — RSiO3.     R  =  Ca,  Mg,  Mn,  Fe,  Al,  chiefly. 

GENERAL  DESCRIPTION. — Monoclinic  crystals.  Usually  short 
and  thick,  with  square  or  nearly  square  cross-section,  or  octagonal 
and  with  well-developed  terminal  planes.  Granular,  foliated  and 
columnar  masses  and  rarely  fibrous.  Color,  white,  various  shades 
of  green,  rarely  bright  green,  and  black. 

CRYSTALLIZATION. — Monoclinic.  ft  =  74°  10'.  Axes  a  :1)  :  c 
—  1.092  :  i  :  0.589. 


FIG.  500. 


Diopside, 
Pitcairn,  N.  Y. 


FIG.  501. 


Rossie,  N.  Y 


FIG.  502. 


J 


Diopside, 
De  Kalb,  N.  Y 


FIG.  503. 


Fassaite. 


Common  forms  :  unit  prism  m,  the  pinacoids  a,  b    and  c,  the 
negative  and,  more  rarely,  the  positive  unit  pyramids  p  and  pt  the 


506 


FIG.  504. 


MINERALOGY. 
FIG.  505. 

^ 

A 


FIG.  506. 


A 


Leucaugite, 
Sing  Sing,  N   Y 


Augite. 


Augite  twin. 


negative   and  positive   pyramids   v  and   v  =  (d  :  6  :  20)  ;   {221} 
Supplement  angles    are:    mm  =  92°  50'  ;  // =  48°  29' ;  pp  = 


59( 
42' 


z/z/  =  68°  42';  -w=  84° 
=  49°  54' ;  <rz>=  65°  21' 


=  33°  49' ;    cp 


Contact  twins,  twinning  plane  a,  Fig.  521,  are  common.  Also 
twin  lamellae  parallel  c,  shown  by  striations  on  the  vertical  faces 
and  by  basal  parting.  Optically  -f .  Axial  plane  b.  Strong 
double  refraction.  Varying  axial  angle.  Usually  not  strongly 
pleochroic. 

Physical  Characters.     H.,  5  to  6.     Sp.gr.,  3.2  to  3.6. 

LUSTRE,  vitreous,  dull  or  resinous.        OPAQUE  to  transparent. 
STREAK,  white  to  greenish.  TENACITY,  brittle. 

COLOR,  white,  green,  black,  brown. 
CLEAVAGE,  prismatic  (angle  87°  10'). 

BEFORE  BLOWPIPE,  ETC. — Variable.  Usually  fuses  easily  to 
dark  glass,  sometimes  to  magnetic  globule.  Not  generally  solu- 
ble in  acids. 

VARIETIES. 

Diopside. — CaMg(SiO3)2.  Usually  white  or  pale-green  to  nearly 
black. 

Common  Pyroxene.—  Ca(Mg.Fe)SiO3.  Chiefly  shades  of  green 
and  black. 

Augite.— CaMg(SiO3)2,  with  (Mg.Fe)(Al.Fe)2SiO6.  Dark-green 
to  black. 

In  addition  there  are  intermediate  members  of  the  isomorphous 
series  such  as  hedenbergite,  (Ca.Fe)(SiO3)2,  grayish-green.  Schef- 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        507 

ferite  containing  up  to  8  per  cent.  MnO,  jeffersonite  containing 

ZnO,  and  diallage,  thin  foliated  pyroxene,  green  or  brown  in  color. 

SIMILAR  SPECIES.  —  Differs  from  amphibole,  as  therein  described. 


ACMITE, 

COMPOSITION.  —  NaFe  (SiO3  )2. 

GENERAL  DESCRIPTION.  —  Occurs  in  long,  prismatic  monoclinic  crystals  of  dark 
green  or  dark  brown  color.  Sometimes  green  on  interior  and  brown  on  exterior  of 
crystal.  In  acmite  these  are  acutely  terminated  and  in  aegirite,  bluntly.  Also 
found  needle-like  and  fibrous.  Streak,  yellowish  gray.  H.,  6-6.5.  Sp.  gr.,  3.5. 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  easily  to  a  black,  slightly  magnetic  globule,  and 
colors  the  flame  yellow.  Only  slightly  affected  by  acids. 

REMARKS.  —  Found  at  Magnet  Cove,  Ark.;  Montreal,  Canada;  Langesund  fiord, 
Norway;  West  Greenland,  etc. 

WOLLASTONITE. 

COMPOSITION.  —  CaSiO3,  SiO2  51.7,  CaO  48.3. 

GENERAL  DESCRIPTION.  —  Cleavable  to  fibrous  white  or  gray  masses.  Also  in 
monoclinic  crystals,  near  pyroxene  in  angle.  Sometimes  compact.  Usually  inter- 
mixed with  calcite.  H.,  4.5  to  5.  Sp.  gr.,  2.8  to  2.9. 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  to  a  white  glass,  color- 
ing the  flame  red.  Soluble  in  hydrochloric  acid,  generally 
effervescing  and  always  gelatinizing. 

SIMILAR  SPECIES.  —  Differs  from  pectolite  and  natrolite 
in  red  flame,  difficulty  of  fusion,  and  absence  of  water.         Harrisville,  N.  Y. 
Tremolite  does  not  gelatinize. 

REMARKS.  —  Occurs  chiefly  in  limestone  contacts  with  pyroxene,  calcite,  garnet, 
etc  Abundant  in  Lewis  and  Warren  Counties,  New  York,  and  at  numerous  localities 
in  Hungary,  Finland,  Norway,  etc. 

ANTHOPHYLLITE. 

COMPOSITION.  —  (Mg.Fe)SiOs,  corresponding  to  enstatite-hypersthene  of  the 
pyroxene  group. 

GENERAL  DESCRIPTION.  —  Gray,  brown  or  green  lamellar  and  fibrous  masses 
often  resembling  asbestos.  Rarely  in  orthorhombic  crystals.  H.,  5.5  to  6.  Sp.  gr., 
3  to  3-2. 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  with  difficulty  to  a  black  enamel  which  is 
attracted  by  the  magnet.  Insoluble  in  acids. 

REMARKS.  —  Occurs  at  Franklin,  Macon  Co.,  N.  C.,  with  corundum,  Kongsberg, 
Norway;  Gedres,  France,  etc.  (gedrite  is  an  aluminous  variety). 

AMPHIBOLE.  —  Hornblende. 

COMPOSITION.  —  RSiO3,  R  being  more  than  one  of  the  elements, 
Ca,  Mg,  Fe,  Al,  Na  and  K. 

GENERAL  DESCRIPTION.  —  Monoclinic  crystals  either  long  with 
acute  rhombic  section  or  shorter  with  six-sided  cross  section. 


508 


MINERALOGY. 


Often  with  ends  like  flat  rhombohedron.  Also  columnar,  fibrous 
and  granular  masses,  rarely  lamellar,  often  radiated.  Colors :  white, 
or  shades  of  green,  brown  or  black. 


FIG.  508. 


FIG.  509. 


FIG.  510. 


Russell,  N.  Y. 


CRYSTALLIZATION.  —  Monoclinic.  Axes  a  \  b  :  c  =  o.  551:1: 
0.294;  /9=73°  58'. 

Common  forms  :  unit  prism  m,  pinacoids  by  c  and  sometimes  a, 
unit  clino-dome  d  and  unit  pyramid  /.  Supplement  angles  are : 
mm=  55°  49';  cm  *=  75°  52';  dd  =  31°  32';  //  =  31°  41'. 
Twinning  as  in  pyroxene. 

Optically  -J--     Axial  plane  b.     Strong  double  refraction.     Often 
strongly  pleochroic. 
Physical  Characters.     H.,  5  to  6.     Sp.  gr.,  2.9  to  3.4. 

LUSTRE,  vitreous  to  silky.  TRANSPARENT  to  opaque. 

STREAK,  white  or  greenish.  TENACITY,  brittle  to  tough. 

COLOR,  white,  gray,  green,  black,  brown,  yellow  and  red. 

CLEAVAGE,  prismatic,  angle  of  124°  11'. 

BEFORE  BLOWPIPE,  ETC. — Varies.      Usually  fuses   easily  to  a 
colored  glass,  which  may  be  magnetic.     Not  affected  by  acids. 
VARIETIES: 

Tremolite. — CaMg3(SiO3)4,  white  to  gray  in  color.  Crystals, 
long-bladed  or  short  and  stout.  Fibrous  masses,  the  fibres  parallel, 
radiating  or  interlaced  and  compact  masses.  Originally  from 
Tremola,  Switzerland.  Sp.  gr.,  2.9  to  3.1. 

Actinolite. — Ca(Mg.Fe)3(SiO3)4,  bright  green  or  grayish-green 
crystals  and  fibrous  masses  and  compact  (nephrite)  as  in  tremolite. 
Sp.  gr.,  3  to  3.2. 

Hornblende* — Ca(Mg.Fe)3(SiO3)4,   with   aluminous   compound. 

*  See  Bulletin  491,  U.  S.  Geol.  Survey,  p.  367. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.        509 

Sometimes  written  as  (Al.Fe)  (F.OH)SiO3,  sometimes  as  an  ortho- 
silicate  isomeric  with  garnet  or  mica.*  Crystals  and  blade-like 
masses  varying  from  light  green  (edenite),  dark  green  (pargasite) 
and  black  (common  hornblende),  but  also  mouse-colored  and 
other  shades. 

Other  varieties  are  cummingtonite  (Mg.Fe)SiO3,  griinerite 
(FeSiO3),  richterite,  containing  5  per  cent,  of  MnO,  etc. 

Nephrite  or  Jade  is  compact  and  extremely  tough,  microscopi- 
cally fibrous,  may  have  composition  of  tremolite  or  actinolite. 

Asbestus  is  in  fine,  easily  separable  fibres,  white,  gray,  or  greenish. 

SIMILAR  SPECIES. — Differs  from  tourmaline  in  cleavage,  crystal- 
line form  and  tendency  to  separate  into  fibres,  from  the  fibrous 
zeolites  in  not  gelatinizing  with  acids,  from  epidote  in  color,  fusi- 
bility and  cleavage.  The  differences  between  it  and  pyroxene  are : 

Amphibole,  prism  angle  and  cleavage  124°;  tough,  often  fibrous, 
rarely  lamellar,  often  blade-like  or  pseudo-hexagonal  crystals, 
usually  simple.  Pyroxene,  prism  and  cleavage  angle  87°;  brittle, 
rarely  fibrous,  often  lamellar,  crystals,  square  or  octagonal  and 
often  complex 

GLAUCOPHANE.— A  sodium  amphibole,  NaAl(SiO3)2(Fe.Mg)SiO3,  blue  in  color 
and  occurring  in  indistinct  monoclinic  prisms  or  in  columnar  and  fibrous  masses. 
Crystals  show  distinctly  different  colors  when  viewed  by  transmitted  light  through 
different  faces.  Cleavage  prismatic.  H.,  6  to  6  5.  Sp  gr  ,  3  to  3.1.  It  is  widely 
distributed  as  glaucophane  schists  in  the  Coast  Ranges  of  California;  Syra,  Greece; 
Zermatt,  Switzerland,  etc. 

CROCIDOLITE.  Blue  Asbestus.— NaFe(SiO3)2  FeSiO3.  Long  delicate  easily 
separable  blue  fibers  and  massive.  H.,  4.  Sp.  gr.,  3.2  to  3.3.  Found  in  Griqualand, 
South  Africa;  Coiling,  Tyrol;  Cumberland,  R.  I.,  and  elsewhere. 

GARNET. 

COMPOSITION.— R"3R'"2(SiO4)3.  R"  is  Ca,  Mg,  Fe  or  Mn. 
R"'  is  Al,  Fe'"  or  Cr,  rarely  Ti. 

GENERAL  DESCRIPTION. — Imbedded  isometric  crystals,  either 
complete  or  in  druses  and  granular,  lamellar  and  compact  masses. 
Usually  of  some  brown,  red  or  black  color,  but  occurring  of  all 
colors  except  blue,  and  harder  than  quartz.  Also  found  in  alluvial 
material  as  rounded  grains. 

*"  Common  hornblende  consists  of  (Ca.Mg.Fe.Na  K  H  Al.Fe)SiO3,  in  which  Ca 
is  about  one  quarter  of  all  the  bases."  "So-called  basaltic  hornblende  is  richer  in 
ferric  iron  than  common  hornblende."  Iddings,  "Rock  Minerals,"  p.  336. 


MINERALOGY. 


CRYSTALLIZATION.  —  Isometric.     Usually  a  combination  of  the 
dodecahedron  d  and  the  tetragonal  trisoctahedron,  n=(a\2a\  20) ; 


FIG.  511. 


FIG.  512. 


FIG.  513. 


{211  j,  Fig.  513,  or  these  as  simple  forms,  Figs.  511,  512,  or  more 
rarely  with  the  hexoctahedron,  s  =  (a  i  fa  :  30) ;  {321),  Fig.  164. 
Optical  Characters. 

Isotropic  but  often  with  local  weak  double  refraction.  Index 
of  refraction  1.739  to  1.878,  hence  in  balsam  the  surface  appears 
very  rough. 

Physical  Characters.     H.,  6.5  to  7.5.     Sp.  gr.,*  3.15  to  4.38. 
LUSTRE,  vitreous  or  resinous.          TRANSPARENT  to  opaque. 
STREAK,  white.  TENACITY,  brittle  to  tough. 

COLOR,  brown,  black,  violet,  yellow,  red,  white,  green. 
CLEAVAGE,  dodecahedral,  imperfect. 

BEFORE  BLOWPIPE,  ETC. — Fuses  rather  easily  to  light  brown 
glass,  except  in  case  of  infusible  chromium  and  yttrium  varieties. 
Insoluble  before  fusion,  but  after  fusion  will  usually  gelatinize  with 
hydrochloric  acid.  Bead  reactions  vary  with  composition. 

VARIETIES. 

Grossularite.—  C^K\2(^iO^)y  White,  pale  yellow,  pale-green, 
brown-red  rose-red. 

Pyrope. — Mg3Al2(SiO4)3  Deep-red  to  nearly  black,  often  trans- 
parent. 

Almandite. — Fe3Al2(SiO4)3.  Fine  deep-red  to  black.  Includes 
part  of  precious  and  of  common  garnet. 

Spessdrtite. — Mn3Al2(SiO4)3.  Brownish-red  to  purplish  hyacinth 
red. 

Andradite. — Ca3Fe2(SiO4)3.  Yellow,  green,  red,  brown,  black. 
Includes  many  of  the  common  garnets. 

Uvarovite  — Ca3Cr2(SiO4)3.     Emerald  green,  small  crystals. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         511 

Schorlomite.— Ca3(Fe.Ti)2(SiTi)4Oi2.     Black. 
Common   Garnet   is   a   mixture   of  grossularite,   almandite  and 
andradite. 

FORMATION   AND    OCCURRENCE    OF   GARNETS. 

Widely  distributed  in  all  classes  of  rocks.  Some  of  the  occur- 
rences are: 

Separations  from  Magma. 

Almandite  in  granite  and  andesite. 
Andradite  in  granite  and  leucite-nephelite  rocks. 
Spessartite  in  granite  and  rhyolite. 
Pyrope  in  peridotites  and  their  serpentines. 
Contacts  with  Limestone. 
Grossularite  and  andradite. 

Metamorphic  Rocks. 

Grossularite  in  limestones. 

Common  garnet  in  schists,  eclogites,  amphibolites,  etc. 

Almandine  in  schists  and  gneisses. 

Andradite  in  gneiss  and  serpentine. 

Spessartite  in  gneiss  and  quartzite. 

Ouvaromte  in  serpentines. 

REMARKS. — Important  localities  for  gem  garnet  are  mentioned  on  p.  567.  In 
Lewis  and  Warren  Counties,  N.  Y.;  Rabun  County,  Ga.,  and  Burke  County,  N.  C., 
garnets  are  mined  for  use  as  an  abrasive. 

VESUVIANITE.— Idocrase. 

COMPOSITION.  —  Ca6[Al(OH,  F)]  Al,(SiOJ6  with  replacement  of 
Ca  by  Mn,  and  Al  by  Fe. 

GENERAL  DESCRIPTION.  —  Brown  or  green,  square  or  octagonal 
prisms  and  less  frequently  in  pyramidal  forms.  Also  in  columnar 
masses  or  granular  or  compact. 

CRYSTALLIZATION.  —  Tetragonal.  Axis  c  =  o.  5  3  7.  Usually  the 
unit  prism  m  with  base  c  and  unit  pyramid  p.  Prismatic  faces 
often  vertically  striated.  Supplement  angles  //  =  50°  39' ;  cp  = 
37°  14'. 

Optical  Characters. 

Uniaxial  —  (rarely  + ) .  Indices  varying  considerably  but  always 
over  1.7,  hence  in  balsam  marked  relief  and  rough  surface.  7  —  0;, 


512 


MINERALOGY. 


o.ooi  to  0.006,  hence  very  low  interference  colors.     Basal  sections 
yield  faint  cross  in  convergent  light. 


FIG.  514. 


FIG.  516 


Monzoni,  Tyrol. 

Physical  Characters.     H.,  6.5.     Sp.  gr.,  3.35  to  3.45. 

LUSTRE,  vitreous  to  resinous.  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  brown  or  green,  rarely  yellow  or  blue     Dichroic. 
CLEAVAGE,  indistinct,  prismatic  and  basal. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  with  intumescence  to  a 
green  or  brown  glass.  At  high  heat  yields  water  in  the  closed 
tube.  Very  slightly  affected  by  hydrochloric  acid,  but  after  igni- 
tion is  dissolved  leaving  a  gelatinous  residue. 

SIMILAR  SPECIES. — The  crystals  and  the  columnar  structure  dis- 
tinguish it  from  epidote,  tourmaline,  or  garnet.  The  colors  are 
not  often  like  those  of  pyroxene. 

FORMATION  AND  OCCURRENCE. — Chiefly  in  contacts  as  at  Mon- 
zoni, Tyrol;  Ala,  Piedmont;  Morelos,  Mexico;  Rumford,  Maine. 
Also  in  blocks  of  limestone  enclosed  in  igneous  rock  as  at  Vesuvius. 
Rarely  in  gneiss  and  schists  and  in  dense  aggregates  in  serpentine. 
A  massive  variety  of  vesuvianite  resembling  jade  has  been  called 
californite. 

THE   OLIVINE   GROUP. 


The  minerals^described  are : 


Forsterite 
Chrysolite 

Fayalite 


Mg2Si04 

(Mg.Fe)2Si04 

Fe2SiO4 


Orthorhombic 
Orthorhombic 
Orthorhombic 


Other  members  of  the  group  are  tephroite,  hortonolite,  knebelite 
and   roepperite.     All   are  orthosilicates   of   magnesium,  calcium, 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         513 

iron  and  manganese,  and  all  orthorhombic  with   the  prismatic 
angle  about  50°,  and  the  unit  brachydome  about  60°. 

FORMATION   AND    OCCURRENCE   OF    OLIVINES. 

Separations  from  Magma. 

Chrysolite  especially  in  the  basic  rocks.  Dunite  is  nearly  pure 
chrysolite.  It  is  essential  in  peridotite  and  norite,  common  as 
microscopic  crystals  in  basalt,  gabbro  and  dolerite  and  as  minor 
accessory  in  andesite,  trachyte,  volcanic  ash  and  ejecta. 

Fayalite  in  nephelin  syenite,  rhyolite  and  granite  pegmatites. 

Contact  or  Regional  Metamorphism. 

Fosterite  in  limestone. 

Chrysolite  in  limestone,  amphibolite,  talc  schist. 

In  Meteorites. 

Chrysolite. 

FORSTERITE.—  Mg2SiO4  in  white  crystals  or  yellowish  or  greenish  imbedded 
grains.  H.,  6  to  7.  Sp.  gr.,  3.2. 

BEFORE  BLOWPIPE,  ETC.  —  Unaltered.  Dissolves  in  hydrochloric  acid  with 
separation  of  a  jelly. 

REMARKS.  —  Not  common  as  pure  material  but  a  component  of  chrysolite.  Occurs 
in  ejected  masses  of  Mt.  Somma  and  in  limestone  at  Kaiserstuhl,  Baden,  and  Rox- 
bury,  Mass.  In  serpentine  at  Snarum,  Norway. 

CHRYSOLITE.—  Olivine,  Peridot. 

COMPOSITION.—  (Mg.Fe)2SiO4, 

GENERAL  DESCRIPTION.  —  Transparent  to  translucent,  yellowish- 
green  granular  masses,  or  disseminated  glassy  grains,  or  olive- 
green  sand.  When  containing  much  iron,  the  color  may  be 
reddish-brown,  or  even,  by  alteration,  opaque-brown  or  opaque- 
green.  Rarely  in  orthorhombic  crystals. 

CRYSTALLIZATION.  —  Orthorhombic.  Axes  d  :  "b  :  c—  0.4657  :  i  : 
0.5865.  Fig.  517  shows  the  pinacoids  a,  b  and  c,  the  unit  forms  of 
pyramid,  prism,  macro  and  brachy  dome  m,  /,  o  and  dy  the  macro 
prism  /=  (a  :  2b  :  co  <:);  {210}  and  macro  pyramid  q  =  (a  :  2b  :  c}\ 

{212}. 

Supplement  angles  are  mm  =  49°  57';   pp  =  40°  5';   co  =  51° 


33' 


34 


MINERALOGY. 


Optical  Characters. 

Biaxial  +.  Axial  plane  (ooi).  Acute  bisectrix  a.  y  1.697, 
a  i. 66 1  hence  in  balsam  rough  with  marked  relief.  y  —  a  =  0.036, 
hence  second  or  third  order  colors  in  thin  sections.  Extinction 
usually  parallel  to  cleavage  lines. 


FIG.  517. 


FIG.  518. 


In  thin  rock  sections,  Fig.  518,  the  outline,  the  cleavage  cracks, 
parallel  (oio)  and  (100)  and  the  frequent  partial  alteration  to 
serpentine  assist  in  its  recognition. 

Physical  Characters,     H.,  6.5  to  7.     Sp.  gr.,  3.27  to  3.57. 
LUSTRE,  vitreous.  TRANSPARENT  to  translucent. 

STREAK,  white  or  yellowish.         TENACITY,  brittle. 
COLOR,  yellowish-green  to  brownish-red. 

BEFORE  BLOWPIPE,  ETC. — Loses  color,  whitens,  but  is  infusible 
unless  proportion  of  iron  is  large,  when  it  fuses  to  a  magnetic  glob- 
ule. Soluble  in  hydrochloric  acid  with  gelatinization  of  silica. 

SIMILAR  SPECIES. — Differs  by  gelatinization  from  green  granular 
pyroxene.  Is  harder  than  apatite  and  less  fusible  than  tourmaline. 
VARIETIES  : 

Hyalosiderite. — A  highly  ferruginous  variety  of  chrysolite,  con- 
taining sometimes  as  high  as  thirty  per  cent,  of  ferrous  oxide. 

Titan-olivine,  a  deep  yellow  or  red  variety  from  Kaiserstuhl, 
Baden,  in  basalt  with  about  five  per  cent,  of  TiO2;  from  Pfunders, 
Tyrol;  and  Zermatt,  Switzerland;  in  talcose  schist. 

REMARKS. — By  alteration  forms  limonite  and  serpentine,  and  the  excess  of 
magnesia  usually  forms  magnesite.  Further  change  may  alter  the  serpentine  to 
magnesite,  leaving  quartz  or  opal.  Found  at  Thetford,  Vt.,  Webster,  N.  C.,  Water- 
ville,  N.  H.,  also  in  Virginia,  Pennsylvania,  New  Mexico,  Oregon.  Prominent 
foreign  localities  are  Vesuvius  and  Mt.  Somma,  the  Swedish  iron  deposits,  the 
Sandwich  Islands,  etc. 

USES. — Transparent  varieties  are  sometimes  cut  as  gems  (see  page  566). 


SILICA    AND    THE  ROCK-FORMING   SILICATES.         515 

FAYALITE. — Fe2SiO4.  In  minute  yellow  to  black  crystals  and  massive.  H., 
6.5.  Sp.  gr.,  4.32. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  to  black  magnetic  globule.  Gelatinizes 
with  acids. 

REMARKS. — Found  in  granite  pegmatites  at  Mourne  Mts.,  Ireland,  and  Rock- 
port,  Mass.;  in  nepheline  syenite  in  Wisconsin;  in  volcanic  rocks  at  Fayal,  Azores; 
Yellowstone  Park;  Lipari  and  elsewhere. 

THE   SCAPOLITE   GROUP. 

The  scapolites  are  regarded  as  a  series  of  isomorphous  mixtures 
oimeionite  (Me)  =  Ca4Al6Si6O25  and  marialite  (Ma),  Na4Al3Si9O24Cl. 
These  end  members  are  not  common,  marialite  occurring  in  a 
volcanic  rock  near  Naples  and  meionite  at  Vesuvius  and  Lake 
Laach. 

The  species  described  are : 

Wernerite  Me: Ma  from  3  :  i  to  i  :  2  Tetragonal 

Mizzonite  Me  :  Ma  from  i  to  2  to  i  :  3  Tetragonal 

FORMATION   AND    OCCURRENCE. 

Not  known  as  primary  minerals  in  igneous  rocks.  Sometimes 
secondary. 

Contacts. 

Common  in  limestone  contacts. 

Metamorphic  Rocks. 

Common  in  schists  and  gneiss  containing  pyroxene  or  epidote, 
also  unaltered  gabbros  by  (pneumatolytic?)  alteration  of  lime 
soda  feldspars.  Found  in  limestones. 

WERNERITE.— Scapolite. 

COMPOSITION. — A  silicate  of  calcium,  and  aluminum,  of  complex 
composition.  It  contains  also  soda  and  chlorine. 

GENERAL  DESCRIPTION.  —  Coarse,  thick,  tetragonal,  "  club- 
shaped,"  crystals,  usually  quite  large  and  dull  and  of  some  gray, 
green,  or  white  color.  Cleavage  surfaces  have  a  characteristic 
fibrous  appearance.  Also  in  columnar  and  granular  masses. 

CRYSTALLIZATION.  —  Tetragonal.  Class  of  third  order  pyramid, 
p.  47.  Axis  c  —  0.438.  Usually  prisms  of  first  order  my  and 
second  order  a,  and  unit  pyramid  /.  Supplement  angle  //  =  43° 

45'. 


MINERALOGY. 


Optical  Characters. 

Uniaxial,  — .  Indices  vary  with  composition,  7  1.597  to  1.555, 
a  1.558  to  1.542,  hence  in  balsam  colorless  grains  or  laths  showing 
cleavage  lines  but  smooth  and  without  relief,  7  —  a  0.013,  hence 


FIG.  519. 


FIG.  520. 


Usual  form. 


Meionite  of  Vesuvius. 


usually  somewhat  brilliant  interference  colors  in  thin   sections. 
Interference  figure  in  basal  sections. 

Distinguished  from  feldspars  by  absence  of  twinning,  from 
quartz  by  cleavage  and  from  both  by  higher  interference  colors. 

Physical  Characters.     H.,  5  to  6.     Sp.  gr.,  2.66  to  2.73. 
LUSTRE,  vitreous  to  dull.  OPAQUE  to  translucent 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  gray,  green,  white,  bluish,  reddish. 
CLEAVAGE.,  parallel  to  both  prisms. 

BEFORE  BLOWPIPE,  ETC. — Fuses  with  intumescence  to  a  white 
glass  containing  bubbles.  Imperfectly  soluble  in  hydrochloric 
acid. 

SIMILAR  SPECIES. — Crystals  often  resemble  those  of  pyroxene; 
the  angles  of  the  terminal  planes  are  conclusive.  Massive  ma- 
terial resembles  feldspar,  but  has  a  characteristic  fibrous  appear- 
ance on  the  cleavage  and  is  more  fusible. 

REMARKS. — Especially  abundant  at  Bolton  and  other  localities  in  Mass.,  and  in 
northern  New  York  and  Canada.  Other  prominent  localities  are  Pargas,  Finland; 
Arendal,  Norway;  and  Lake  Baikal. 

MIZZONITE.  Dipyre. — With  54  to  57  p.  c.  SiO2,  corresponding  to  Me  :  Ma 
=  i  :  2  to  Me  :  Ma  =1:3. 

In  slender  square  prisms  with  essentially  the  characters  of  wernerite. 

Found  at  Vesuvius;  in  the  Pyrenees;  at  Bamle,  Norway;  Canaan,  Conn.;  and 
Ripon,  Quebec 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        517 


THE   ANDALUSITE   GROUP. 


The  minerals  described  are : 


Andalusite 

Sillimanite 
Cyanite 


Al(AlO)SiO4 
Al(A10)SiO4 
(A10)2SiO3 


Orthorhombic 
Orthorhombic 
Triclinic 


These  minerals  with  identical  chemical  composition,  for  which 
the  simplest  empirical  formula  would  be  A^SiOs,  are  generally 
regarded  as  different  in  chemical  structure  and  the  formulae  written 
as  above.  Sillimanite  is  the  most  stable  under  the  action  of  heat, 
the  others  changing  to  it. 

FORMATION   AND    OCCURRENCE   OF   ANDALUSITE    GROUP. 

In  Igneous  Rocks. 

Sillimanite  and  andalusite  occasionally  occur  in  granite,  but 
according  to  Iddings*  the  andalusite  is  accompanied  by  inclusions 
of  sedimentary  rock. 

Contacts. 

Andalusite  (chiastolite)  usually  without  sillimanite  in  contact 
zone  of  schists  and  slates  with  intrusions.  Cyanite  occasional. 

Metamorphic  Rocks. 

Andalusite,  sillimanite  and  cyanite  in  some  gneisses  and  mica 
schists. 

OPTICAL   DETERMINATION   OF   THE   ANDALUSITE   GROUP. 
All  are  biaxial  and  with  high  indices  showing  in  balsam  high 
relief  and  rough  surface. 

Useful  characters  may  tabulate  as  follows: 


Elongation  . 

Indices  Refraction. 

Usual  Appearance  in  Sections. 

Y 

a 

y—  a 

Andalusite  

+ 

1.643 
1.676 
1.729 

1.632 
1.656 

I.7I7 

O.OII 
O.02I 
O.OII 

Short  prisms,  square  sections. 
Slender  needles  and  aggregates, 
Bladed  crystals,  six-sided  sec- 
tions. 

Sillimanite  
Cyanite  .  .  . 

Between  each  other  the  appearance,  the  sign  of  elongation,  the 
relatively  bright  interference  colors  of  sillimanite  and  the  large- 
angled  interference  figure  and  oblique  (30°)  extinction  on  the  easy 

*  Rock  Minerals,  p.  290. 


MINERALOGY. 


cleavage  (100)  of  cyanite,  generally  suffice.  The  symmetrically 
arranged  carbonaceous  inclusions  in  andalusite,  Fig.  217,  and  the 
needle  aggregates  of  sillimanite  Fig  521  also  assist. 


FIG.  521. 


Sillimanite  needle  aggregate. 

In  both  andalusite  and  sillimanite  the  axial  plane  is  (oio)  and 
the  acute  bisectrix  is  c,  the  former  giving  a  very  large  angle,  the 
latter  a  small  angle. 

ANDALUSITE.— Chiastolite. 

COMPOSITION.— Al(AlO)SiO4f  (A12O3  63.2,  SiO2  36.8  per  cent.) 
GENERAL  DESCRIPTION. — Coarse,  nearly  square  prisms  of  pearl 
gray  or  pale  red  color,  or  in  very  tough,  columnar  or  granular 
masses.  An  impure  soft  variety  (chiastolite)  occurs  in  rounded 
prisms,  any  cross  section  of  which  shows  a  cross  or  checkered 
figure,  due  to  the  symmetrical  deposition  of  the  impurities,  p.  80. 


FIG.  522. 


FIG.  523. 


SILICA   AND    THE  ROCK-FORMING  SILICATES 


519 


CRYSTALLIZATION.  — Orthorhombic.  Axes  a  :  b  :  c  =  0.986  :  i  : 
0.702.  Usually  either  the  unit  prism  m,  and  base  r,  or  these  with 
the  unit  brachy  dome  d.  Supplement  angles  are  mm  =  89°  12'  , 
dd=7o°  10'. 

Physical  Characters.     H.,  7  to  7.5.     Sp.  gr.,  3.16  to  3.20. 
LUSTRE,  vitreous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle  to  tough. 

COLOR,  rose-red,  flesh-red,  violet,  pale  green,  white,  pearl-gray. 
CLEAVAGE,  prismatic,  imperfect  at  angle  of  90°  48' 

BEFORE  BLOWPIPE,  ETC. — Infusible.  In  powder  becomes  blue 
with  cobalt  solution.  Insoluble  in  acids. 

REMARKS. — It  occurs  as  stated  on  p.  517.  It  alters  rather  readily  to  cyanite  or 
kaolin.  Found  in  many  localities  in  the  New  England  States,  also  in  Pennsylvania 
and  California.  It  has  been  recognized  in  granite  in  Cornwall  and  Saxony.  Large 
crystals  are  found  at  Lisens,  Tyrol,  and  transparent  crystals  in  Minas  Geraes,  Brazil. 

SILLIMANITE  or  FIBROLITE. 

COMPOSITION.— Al(AlO)SiO4. 

GENERAL  DESCRIPTION. — Long,  almost  fibrous  orthorhombic  crystals,  and  fibrous 
or  columnar  masses  of  brown  or  gray  color. 

PHYSICAL  CHARACTERS.— Transparent  to  translucent.  Lustre,  vitreous.  Color, 
brown,  gray,  greenish.  Streak,  white.  H.,  6  to  7.  Sp.  gr.,  3.23  to  3.24.  Tough. 
Cleavage,  parallel  to  brachy  pinacoid. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  becomes  dark  blue  with  cobalt  solution.  In- 
soluble in  acids. 

REMARKS. — Chiefly  found  in  mica  schist,  gneiss,  etc.     Sometimes  with  andalusite. 

USES. — In  the  stone  age  it  was  used  for  tools,  weapons,  etc.,  being  second  only  to 
jade  in  toughness. 

CYANITE.  — Kyanite. 

COMPOSITION.  —  (AlO)2SiO3,  probably  a  basic  me- 
tasilicate. 

GENERAL  DESCRIPTION.  —  Found  in  long  blade- 
like  triciinic  crystals,  rarely  with  terminal  planes. 
The  color  is  a  blue,  deeper  along  the  center  of  the 
blades,  and  at  times  passes  into  green  or  white. 

Physical  Characters.     H.,  5  to  7.     Sp.  gr.,  3.56  to  3.67. 
LUSTRE,  vitreous.  TRANSLUCENT  to  transparent. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  blue,  white,  gray,  green  to  nearly  black. 
CLEAVAGE,  parallel  to  the  three  pinacoids. 


520 


MINERALOGY. 


BEFORE  BLOWPIPE,  ETC — Infusible,  with  cobalt  solution  be- 
comes blue.  Insoluble  in  acids. 

STAUROLITE. 

COMPOSITION.— Fe(AlO)4(AlOH)(SiO4)2,  but  varying.  May  con- 
tain Mg  or  Mn. 

GENERAL  DESCRIPTION. — Dark  brown  to  nearly  black  ortho- 
rhombic  prisms  often  twinned,  or  in  threes,  crossing  at  90°  and 
I2O°.  Surfaces  bright  if  unaltered.  Very  hard. 

CRYSTALLIZATION. — Othorhombic.  Axes  d  :  b  :  c  —  0.473  :  l  : 
0.683.  Usual  forms :  unit  prism  m,  unit  dome  o  and  pinacoids  b 
and  c.  Frequently  in  twins  crossed  nearly  at  right  angles,  Fig. 
566,  or  nearly  at  60°,  Fig.  567. 

Supplement  angles  are  :  mm  =  50°  40' ;  co  =  55°  14'. 

Optical  Characters. 

Biaxial  +  ,  axial  plane  (100),  acute  bisectrix  c,  hence  inter- 
ference figure  (large  angle)  in  basal  section. 

Indices  of  refraction  high,  y  =  1.746,  a  =  1.736,  hence  marked 
relief  in  balsam.  7  —  a  =  o.oio,  hence  interference  colors  like 
quartz.  Extinctions  parallel  or  symmetrical  to  outlines.  Elonga- 
tion -f- .  Distinctly  pleochroic  in  shades  of  brown. 


FIG.  525. 


FIG.  526. 


FIG.  527. 


Physical  Characters.     H.,  7  to  7.5.     Sp.  gr.,  3.65  to  3.75. 
LUSTRE,  resinous  or  vitreous.  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  dark  brown,  blackish-brown,  gray  when  weathered. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  except  when  manganlfer- 
ous.     Partially  soluble  in  sulphuric  acid. 

REMARKS. — Occurs  chiefly  in  gneiss  and   mica  schist;   and  rarely  as  a  contact 
mineral  in  clay  slates.     Abundant  at  Claremont,  Grantham,  and  Lisbon,  N.  H.,. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         521 

at  Windham,  Me.,  Chesterfield,  Mass.,  Litchfield,  Conn.,  and  several  other  locali- 
ties in  New  England.  Also  in  New  York,  North  Carolina,  Georgia,  and  Pennsyl- 
vania. Foreign  localities  are  Mt.  Campione,  Switzerand;  Greiner,  Tyrol;  Brittany; 
Ireland. 

BERYL,   TOPAZ   AND   TOURMALINE. 

Beryl  Be3Al2(SiO3)6  Hexagonal 

Topaz  Al(Al(O.F2))SiO4  Orthorhombic 

Tourmaline  Ri8B2(SiO5)4  Hexagonal 

While  not  a  group  in  any  chemical  or  crystallographic  sense, 
the  minerals  are  conveniently  discussed  together  as  to  formation 
and  occurrence  and  optical  properties. 

FORMATION   AND    OCCURRENCE. 

Topaz  and  tourmaline  are  due  to  pneumatolytic  action;  beryl 
is  so  in  part,  perhaps  wholly.     They  occur  often  associated.     The 
chief  occurrences  are : 
Igneous  Rocks. 

Beryl,  topaz  and  tourmaline  in  granites  and  especially  in  pegma- 
tites. Examples:  Mourne  Mt.,  Ireland;  Elba,  Finbo,  Sweden; 
Black  Hills,  Dakota;  Grafton,  N.  H. 

Topaz  in  Rhyolite,  Nathrop,  Colorado;  Thomas  Range,  Utah. 
Contacts. 

Iron  tourmaline  between  schists  and  granites. 

Magnesium  tourmaline  in  limestone  contacts. 
Veins. 

Topaz  and  tourmaline  almost  invariably  present  in  tin  veins 
and  common  in  other  high  temperature  deposits. 

Beryl  (emerald)  of  Muzo,  Colombia,  in  calcite  veins  in  sediments, 
probably  derived  from  nearby  pegmatites. 
Replacements. 

Topaz  metasomatically  replaces  country  rock,  forming  topaz 
rocks  near  the  tin  veins  of  Schneckenstein,  Saxony;  and  Mount 
Bischoff,  Tasmania. 

Tourmaline  similarly  in  tin  regions,  as  at  Cornwall,  replaces 
mica  and  feldspar,  forming  tourmaline  granites,  luxullianite,  etc. 
Metamorphic  Rocks. 

Beryl  and  tourmaline  occur  in  mica  schists,  and  gneiss  and 
tourmaline  in  clay  slates. 

*  Beyschlag,  Vogt  and  Krusch  (Truscott),  p.  415. 


522 


MINERALOGY. 
OPTICAL   CHARACTERS. 


y 

a 

y  —  a 

Elonga- 
tion. 

Beryl 

Uniaxial  (—  ) 

.572  to  1.578 

.567  to  1.573 

O.OO6 

C—  ) 

Topaz               .    . 

Biaxial  (+) 

.617  to  1.637 

.609  to  1.629 

O.OO8 

(+) 

Tourmaline: 
Lithium  
Magnesium.  .  . 
Iron  

Biaxial  (—  ) 
Biaxial  (—  ) 
Biaxial  (—  ) 

.637  to  1.650 
.631  to  1.653 
.642  to  1.685 

.620  to  1.625 
.612  to  1.629 
.622  to  1.651 

O.OI4  to  O.O2I 

0.019  to  0.024 

0.020  tO  O.O34 

-    (-) 
(-) 
(-) 

For  topaz  the  axial  plane  is  the  easy  basal  cleavage  .001  and 
the  acute  bisectrix  is  c. 

In  thin  sections  in  balsam  relief  is  low  in  beryl,  medium  in  topaz, 
marked  in  tourmaline. 

Interference  colors  in  thin  sections  are  evidently  very  low  in 
beryl,  about  like  quartz  in  topaz  and  while  bright  in  tourmaline 
may  be  masked  by  the  strong  absorption  (greatest  at  right  angles 
toe). 

Pleochroism  is  strong  in  tourmaline  and  little  noticed  in  the 
others. 

BERYL.  —Emerald,  Aquamarine. 

COMPOSITION.*—  Be3Al2(SiO3)6. 

GENERAL  DESCRIPTION.  —  Hexagonal  prisms,  from  mere  threads 
to  several  feet  in  length.     Usually  some  shade  of  green.     Some- 
times in  large  columnar  or  granular  masses.     Harder  than  quartz. 
FIG.  528.  FIG.  529.  FIG.  530. 


CRYSTALLIZATION.  —  Hexagonal.  Axis  c  =  0.499.  Usually  prism 
m  with  base  c,  sometimes  with  unit  pyramid  /  or  second  order 
form  e=(2a:2a:a:  2r)  ;  {1121}.  Supplement  angles  cp  = 
29°  56';  ^  =  44°  56'. 


*  Sodium,  lithium  and  cesium  may  replace  beryllium. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         523 

Physical  Characters.     H.,  7.5  to  8.     Sp.  gr.,  2.63  to  2.8. 

LUSTRE,  vitreous.  TRANSPARENT  to  nearly  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  emerald  to  pale-green,  blue,  yellow,  white,  red,  colorless. 

CLEAVAGE,  imperfect  basal  and  prismatic. 

BEFORE  BLOWPIPE,  ETC.— Fuses  on  thin  edges,  often  becom. 
ing  white  and  translucent.  Slowly  dissolved  in  salt  of  phosphorus 
to  an  opalescent  bead.  Insoluble  in  acids. 

VARIETIES. 

Emerald. — Bright  emerald  green,  from  the  presence  of  a  little 
chromium. 

Aquamarine. — Sky-blue  to  greenish-blue. 

Goshenite. — Colorless. 

SIMILAR  SPECIES. — Harder  than  apatite,  quartz  or  tourmaline. 
Differs  in  terminal  planes  from  quartz  and  in  form  from  chryso- 
beryl.  Lacks  distinct  cleavage  of  topaz.  Rarely  massive.  Usu- 
ally some  shade  of  green. 

REMARKS. — Beryls  are  especially  abundant  at  Acworth  and  Graf  ton,  *  N.  H.; 
Royalston,  Mass.;  Paris  and  Stoneham,  Me.;  Alexander  County,  N.  C.;  the 
Black  Hills  of  South  Dakota,  and  Litchfield,  Conn.  Famous  foreign  localities  are 
Muzo,  Colombia;  the  Urals,  Brazil,  India  and  Australia. 

USES. — Emerald  and  aquamarine  are  cut  as  gems  (see  p.  559). 

TOPAZ. 

COMPOSITION.— Al12Si6O25F10  or  Al(Al(O.F2))SiO4. 

GENERAL  DESCRIPTION. — Hard,  colorless  or  yellow  transparent 
orthorhombic  crystals  with  easy  basal  cleavage.  Also  massive  in 
columnar  aggregates,  and  as  rolled  fragments  and  crystals  in  allu- 
vial deposits. 

CRYSTALLIZATION.  —  Orthorhombic.     ^1^:^  =  0.529:1: 0.477. 

Prisms  often  vertically  striated.  Crystals  rarely  doubly  termi- 
nated. The  predominating  forms  are  the  unit  prism  my  brachy 

prism  /  =  (2%  :  ~b  :  oo  c)  ;  { 1 20}  (with  predominance  of  /  the  section 
is  often  nearly  square);  base  c,  unit  pyramid  /  and  dome /= 
(oo  d  :  b\  2r);  {021}. 

Supplement  angles  are :  mm—  55°  43';  //=  93°  1 1' ;  //  =  38°  ; 
/"(top)  =  87°  1 8'. 

*  Those  at  Acworth  and  Grafton  are  sometimes  of  immense  size.  One  crystal, 
near  the  railroad  station  of  Grafton  Centre,  measures  3  feet  4  inches  by  4  feet  3 
inches  on  horizontal  section,  and  is  exposed  for  over  5  feet. 


524 


FIG.  531- 


MINERALOGY. 
FIG.  532. 


FIG.  533. 


Omi,  Japan. 

Physical  Characters.    H.,  8.     Sp.  gr.,  3.4  to  3.65. 

LUSTRE,  vitreous.  TRANSPARENT  to  nearly  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,   colorless,  yellow,  pale-blue,  green,  white,  pink. 
CLEAVAGE,  basal  perfect. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  but  yellow  varieties  may 
become  pink.  With  cobalt  solution  the  powder  becomes  blue. 
Slowly  dissolved  in  borax.  If  powdered  and  heated  with  previ- 
ously fused  salt  of  phosphorus  in  open  tube  the  glass  will  be 
etched.  Insoluble  in  acids. 

REMARKS. — Fine  crystals  are  obtained  in  Colorado,  Utah,  and  Maine  and  well- 
known  foreign  localities  are  Minas  Geraes,  Brazil;  the  Urals;  Mexico;  Japan,  and 
the  tin  mines  of  Saxony. 

For  topaz  as  a  gem  mineral  see  page  564. 

TOURMALINE.— Schorl. 

COMPOSITION. — R18B2(SiO6)4.     R  chiefly  Al,  K,  Mn,  Ca,  Mg,  Li. 

GENERAL  DESCRIPTION. — Prismatic  crystals,  the  cross  sections 
of  which  frequently  show  very  prominently  a  triangular  prism. 
Color,  usually  some  dark  smoky  or  muddy  tint  of  black,  brown  or 
blue,  also  bright  green,  red,  and  blue,  or  rarely  colorless.  Some- 
times the  centre  and  outer  shell  are  different  colors,  as  red  and 
green.  Sometimes  the  color  is  different  at  two  opposite  ends. 
Occurs  also  columnar  in  bunches  or  radiating  aggregates  and  in 
compact  masses. 

CRYSTALLIZATION.  —  Hexagonal.  Hemimorphic  class,  p.  52. 
Axis  c  =  0.448. 

Prevailing  forms :  trigonal  prism  m,  second  order  prism  a,  tri- 
gonal pyramids  /  (unit)  and  /=  (a  :  co  a  :  a  :  2c\  {2021 }.  Sup- 
plement angles  are  :  pp  =  46°  52'  ;/*=  77°  ;  mp  =  62°  40'. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         525 
FIG.  534.  FIG.  535.  FIG.  536. 


Physical  Characters.     H.,  7  to  7.5.     Sp.  gr.,  2.98  to  3.20. 
LUSTRE,  vitreous  or  resinous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  black,  brown,  green,  blue,  red,  colorless. 
CLEAVAGE,  difficult,  parallel  to  R  and  i -  2. 

BEFORE  BLOWPIPE,  ETC. — Usually  fuses,  sometimes  very  easily. 
With  a  paste  of  KHSO4,CaF2  and  water  it  yields  a  green  flame. 
Insoluble  in  acids,  but  after  strong  ignition  gelatinizes. 

SIMILAR  SPECIES. — Differs  from  hornblende  in  hardness,  crystal- 
line form  and  absence  of  prismatic  cleavage.  Differs  from  garnet 
or  vesuvianite  in  form,  difficult  fusion,  and  green  flame. 

REMARKS. — The  chemical  formula  is  not  decided.  Others  suggested  are 
AlsR'sSieBsOsi.  AluR'uSieBsOsi.  AlyR'sSieBsOai.  Strictly  tourmaline  represents 
an  isomorphous  group  with  three  great  types. 

Iron  Tourmaline. — The  common  black  variety,  which  alone  is  important  as  a 
rock-making  mineral.  Associated  commonly  with  muscovite  or  biotite. 

Magnesium  Tourmaline. — Often  found  in  limestone  or  dolomite,  with  phlogopite 
as  the  accompanying  mica. 

Alkali  Tourmaline. — Contains  lithium  or  sodium,  sometimes  potassium  in  less 
amount.  Found  in  pegmatites,  with  muscovite  and  lepidolite.  Often  transparent 
red,  green,  blue,  etc. 

Famous  localities  are  Gouverneur  and  Pierrepont,  N.  Y.;  Paris  and  Hebron, 
Maine;  Pala,  California;  foreign  localities  are  Urals,  Brazil,  Elba  and  Carinthia. 

For  tourmaline  as  a  gem  mineral,  see  p.  564. 

TITANITE.  —  Sphene. 

COMPOSITION.  —  CaSiTiO5. 

GENERAL  DESCRIPTION.  —  Brown,  green  or  yellow,  wedge-shaped 
or  tabular  monoclinic  crystals,  with  adamantine  or  resinous  lustre. 


526 


MINERALOGY. 


CRYSTALLIZATION.  —  Monoclinic.    ft  =  60°  FlG-  S37- 

17'.  Axestf  :  ~b  :  c  =  0.755  :  I  :  0.854.  Crys- 
tals very  varied.  The  most  common  forms 
are  :  pinacoids  c  and  a,  unit  prism  m,  negative 
unit  pyramid  /,  domes  x  =  (a  :  oo  "b  :  y2c]  ; 
{102},  and  s=  (_oo  a  :  7  :  2r);  {021},  and  the 
pyramid  /  =  (a  :  b  :  fa)  ;  {112}.  Supplement 
angles  are:  mm  =  66°  29'  ;  //  =  43°  49'  ;  //=  46°  f  . 

Optical  Characters. 

Biaxial  +  .  Axial  plane  (oio).  Interference  figure  character- 
ized by  large  differences  in  axial  angle  for  different  colors,  and 
broad  rainbows  instead  of  black  hyperbola. 

Indices  very  high,  7  2.009,  «  1.887,  7  ~  «»  0.1214.     In  sections 
interference  colors  usually  very  high  but  in  some  sections  grays 
of  i°  order.     Extinction  angles  not  characteristic. 
Physical  Characters.     H.,  5  to  5.5.     Sp.  gr.,  3.4  to  3.56. 

LUSTRE,  adamantine  or  resinous.        TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  brown  to  black,  yellow,  green,  rarely  rose-red. 

CLEAVAGE,  prismatic  easily,  pyramidal  less  easily. 

.  BEFORE  BLOWPIPE,  ETC.  —  Fuses,  with  intumescencet  to  a  dark 
glass,  sometimes  becoming  yellow  before  fusion.  In  sal  of  phos- 
phorus after  reduction,  the  bead  is  violet.  Partly  soluble  in 
hydrochloric  acid,  completely  so  in  sulphuric  acid. 

FORMATION  AND  OCCURRENCE  —  Crystallizes  from  magma  as  ac- 
cessory mineral  chiefly  in  the  plutonic  rocks,  such  as  hornblende, 
granite,  syenite,  and  elaeolite-syenite,  but  also  in  trachytes,  etc. 

Secondary  in  metamorphic  rocks,  in  rocks  carrying  rutile  or 
ilmenite,  in  clefts,  gneiss,  or  schists  or  in  granular  limestone. 

REMARKS.  —  Famous  localities  are  Tavetsch,  Switzerland;  Pfitsch,  Tyrol;  Renfrew, 
Ontario,  and  other  Canadian  apatite  veins;  Diana,  New  York;  Brewsters,  N.  Y.: 
Bridgewater,  Pa.,  and  Magnet  Cove,  Ark. 

For  titanite  as  a  gem  see  p.  566. 

THE   EPIDOTE   GROUP. 

The  minerals  described  are  : 

Ca2Al2(Al.OH)(SiO4)3  Orthorhombic 

Ca2Al2(A1.0H)(Si04)3  Monoclinic 

Ca2(Al.Mn)2(Al.OH)(SiO4)3  Monoclinic 

(Ca.Fe)2(Al.Ce.Fe)2(Al.OH)(SiO4)3  Monoclinic 


Epidote 

Piedmontite 
AUanite 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         527 


FORMATION   AND    OCCURRENCE    OF   EPIDOTE    GROUP. 

Separation  from  Magma. 

Allanite  is  an  accessory  mineral  in  granite,  pegmatites,  and  in 
other  igneous  rocks  in  minor  amounts. 

Epidote  is  rare  but  sometimes  is  found  intergrown  with  allan- 
ite  and  occasionally  alone,  as  in  granite  of  Ilchester,  Md. 

Secondary  in  Igneous  Rocks. 

Epidote  is  widely  distributed  as  an  alteration  of  the  feldspars 
and  other  minerals  rich  in  calcium,  piedmontite  is  secondary  in 
the  original  locality,  the  zoisite  in  Piedmont  granite  is  probably 
secondary  and  it  accompanies  epidote  in  altered  gabbros  (sauss- 
urite). 

Contacts. 

Epidote  in  contacts  with  limestone  and  other  rocks  high  in 
calcium. 

Metamorphic  Rocks. 

Zoisite  is  especially  found  in  metamorphosed  igneous  rocks  high 
in  calcium,  as  amphibolite  or  glaucophane  schist. 

Epidote  is  common  in  clefts  and  hollows  of  gneiss  and  schists 
(forms  with  quartz  the  rock  epidosite). 

Ore  Beds. 

Zoisite  in  sulphides,  epidote  rarely. 

OPTICAL    DETERMINATION   OF   EPIDOTE    GROUP. 

The  ready  distinctions  between  members  of  the  group  lie  in  the 
color,  pleochroism,  interference  colors  and  extinctions. 


Color. 

Pleochroism. 

Interference  Colors. 

Extinctions 
with  Cleavages. 

Zoisite  
Epidote  

Piedmontite  . 
Allanite  

Colorless 
|'  Yellowish  to    "j 
•j  yellow-brown  > 
(.  greenish           J 
Red 
Brown 

None 
Strong  if  colored 

Red  to  yellow 
Strong 

Very  low  order 
Often  high  orders 

Medium 

Parallel 
Varying  angle 

Varying  angle 

In  general  high  relief  and  rough  surface.  All  are  biaxial.  Epidote 
differs  from  pyroxene  in  the  fact  that  the  plane  of  the  optic  axis 
is  perpendicular  to  the  cleavage  cracks. 


528  MINERALOGY. 

ZOISITE.  — Thulite. 

COMPOSITION.  —  Ca2Al2(  Al.OH)  (SiO4)3. 

GENERAL  DESCRIPTION. — Gray  or  green  and  rose  red  (thulite)  columnar  and 
fibrous  aggregates.  More  rarely,  deeply  striated  orthorhombic  prisms  with  indistinct 
terminations  and  perfect  cleavage  parallel  to  the  brachy-pinacoid. 

PHYSICAL  CHARACTERS.  —  Transparent  to  opaque.  Lustre,  vitreous  to  pearly. 
Color,  white,  gray,  brown,  green,  pink  and  red.  Streak,  white.  H.,  6-6.5.  Sp.  gr-> 
3- 2S-3- 35-  Optically  -f  . 

BEFORE  BLOWPIPE,  ETC.  —  Swells  up  and  fuses  easily  to  a  glassy  mass  which  does 
not  readily  assume  globular  form.  Not  affected  by  HC1  before  ignition,  but  after  igni- 
tion it  is  decomposed  with  formation  of  jelly. 

REMARKS. — Found  at  Ducktown,  Tenn.,  Chesterfield,  Mass.,  Uniontown,  Pa.,  and 
many  other  localities. 

EPIDOTE. 

COMPOSITION.  —  Ca2Al2(AlOH)(SiO4)3  with  some  iron  replacing 
aluminum. 

GENERAL  DESCRIPTION.  —  Coarse  or  fine  granular  masses  of 
peculiar  yellowish-green  (pistache  green)  color,  sometimes  fibrous- 
Also  in  monoclinic  crystals  and  columnar  groups,  from  yellow- 
green  to  blackish-green  in  color. 

CRYSTALLIZATION. — Monoclinic.       0  = 
FIG.  538.  64°  37'.    Axes  a  :  b  :  c  =  1.579  :  I  :  1,804. 

Common  forms  :  m  =  unit  prism,  a  and  c 
Pmac°ids,    p   unit    pyramid    and    o    unit 
dome.    Supplement  angles  are  mm  =  109° 
56';    ca  =  64°   37';    co  =  63°   42'.     Crys- 
tals extended  in  the  direction  of  the  ortho-axis,  in  the  zone  of 
which  are  two  cleavages  (ooi)  and  (100)  at  64°  37'  to  each  other. 
Physical  Characters.     H.,  6  to  7.     Sp.  gr.,  3.25  to  3.5. 
LUSTRE,  vitreous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  yellowish-green  to  nearly  black  and  nearly  white,  also 

red  and  gray.  CLEAVAGE,  basal,  easy. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  with  intumescence  to  a 
dark,  usually  slightly  magnetic,  globule.  At  high  heat  yields 
water.  Slightly  soluble  in  hydrochloric  acid,  but  if  previously 
ignited,  it  dissolves,  leaving  gelatinous  silica. 

REMARKS. — Famous  localities  for  crystallized  epidote  are  Untersulzbachthal, 
Tyrol;  Bourg  d'Oisans,  Dauphiny;  Warren,  N.  H.;  Alaska. 

PIEDMONTITE. — Similar  in  angle  to  epidote,  but  with  5  to  15  p.  c. 
Color  reddish  brown  and  reddish  black.     H.  =  6.5.     G.  =  3.404. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         529 

Known  chiefly  in  the  occurrence  with  braunite  at  St.  Marcel,  Piedmont,  and  the 
piedmontite  schists  of  Japan. 

ALLANITE. 

COMPOSITION. — Analogous  to  epidote,  but  a  silicate  of  the  cerium  and  yttrium 
groups  with  lime  and  iron. 

GENERAL  DESCRIPTION. — Pitch  black  or  brownish  embedded  veins  and  masses 
and  flat  tabular  or  prismatic  (like  a  nail)  monoclinic  crystals. 

PHYSICAL  CHARACTERS. — Opaque.  Lustre,  submetallic  or  pitch-like.  Color,  pitch 
black  or  brown.  Streak,  nearly  white.  H.,  5.5  to  6.  Sp.  gr.,  3.5  to  4.2.  Brittle. 

BEFORE  BLOWPIPE,  ETC. — Fuses  very  easily,  becoming  strongly  magnetic,  and  at 
high  temperature  yielding  water.  Usually  gelatinizes  with  hydrochloric  acid,  but 
after  ignition  is  insoluble. 

REMARKS. — Found  in  Sweden,  Norway,  Greenland  and  the  Urals.  In  this 
country  at  Baringer  Hill,  Texas;  Amherst  Co.,  Virginia;  South  Mountain,  Penn., 
and  many  other  localities. 

IOLITE.— Dichroite,  Cordierite. 

COMPOSITION.— Mg3(Al.Fe)6(SiO4)4(SiO3)4. 

GENERAL  DESCRIPTION. — Short,  six-  or  twelve-sided  orthorhombic  prisms  and 
massive,  glassy,  quartz-like  material.  Usually  blue  in  color.  The  color  is  often  deep 
blue  in  one  direction  and  gray  or  yellow  in  a  direction  at  right  angles  with  the  first. 

PHYSICAL  CHARACTERS. — Transparent  or  translucent.     Lustre,  vitreous.     Color, 
light  to  smoky  blue,  gray,  violet  or  yellow.     Dichroic.     Streak,  white.     H.,  7  to  7.5. 
Sp.  gr.,  2.6  to  2.66.     Brittle.     Cleaves  parallel  to  brachy-pinacoid. 
OPTICAL  CHARACTERS. 

Colorless  or  bluish  with  low  relief  in  balsam  (7  1.54  to  1.56).  If  blue  is  pleochroic. 
In  thicker  material  pleochroism  very  marked. 

Birefringence  weak  (0.009),  hence  colors  like  quartz.  Extinction  parallel  cleavage 
cracks. 

BEFORE  BLOWPIPE,  ETC. — Fuses  with  difficulty,  becoming  opaque.  With  cobalt 
solution  becomes  blue-gray.  Partially  soluble  in  acids. 

REMARKS. — Occurs  in  gneis^  and  sometimes  in  granite,  rarely  in  volcanic  rocks,  and 
is  formed  by  contact  with  igneous  matter.  It  is  easily  altered  to  a  soft  lamellar  or 
fibrous  material  of  green  or  yellow  color,  and  is  rarely  found  entirely  unaltered. 

THE   ZEOLITE   GROUP. 

The  minerals  described  are: 

ZEOLITES   PROPER.* 

Analcite  NaAl(SiO3)2  +  H2O  Isometric 

Natrolite  Na2Al(AlO)(SiO3)3  +  2H2O  Orthorhombic 

Chabazite  (Ca.Na2)Al2(SiO3)4  +  6H2O  Hexagonal 

Stilbite  H4(Na2Ca)Al2(SiO3)6  +  4H2O  Monoclinic 

Heulandite  H4CaAl2(SiO3)6  +  3H2O  Monoclinic 

Harmotome  BaAbSisO^sH^O  Monoclinic 

Thomsonite  (CaNa2)2AUSi4Oi65H2O  Orthorhombic 

*  To  these  may  be  added  ptilolite,  mordenite,  brewsterite,  epistilbite,  phillipsite, 

gismondite,  laubanite,  gmelinite,  levynite,  faujasite,  edingtonite,  mesolite,  erionite, 

wellsite,  and  perhaps  other  species. 
35 


53o  MINERAL  OGY. 

ZEOLITE   ANNEX.* 

Apophyllite  Hi4K2Ca8(SiO3)i6  +  9H2O  Tetragonal 

Pectolite  HNaCa2(SiO3)3  Monoclinic 

Prehnite  H2Ca2Al2(SiO4)3  Orthorhombic 

Datolite  Ca(B.OH)SiO4  Monoclinic 

FORMATION  AND   OCCURRENCE    OF   ZEOLITES. 

The  zeolites  are  of  especial  interest  from  their  frequent  connec- 
tion with  native  copper,  silver,  magnetite,  pyrrhotite  and  other 
ores.  Their  presence  appears  to  prove  formation  at  low  tempera- 
tures and  it  is  believedf  they  may  represent  a  last  stage  of  cooling 
and  a  crystallization  from  residual  solutions.  The  occurrences 
are  of  the  following  types: 
Separation  from  Magma  in  Plutonic  Rocks. 

Analcite  is  the  chief  constituent  of  a  dike  at  Heron  Bay,  L.  S., 
and  occurs  in  sodalite  syenite  of  Butte,  Mont.,  and  certain  rocks 
of  Pikes  Peak,  Col. 

Filling  Blowholes  and  Crevices  in  Basic  Lava. 

This  is  the  principal  occurrence  but  whether  secondary  entirely 
or  largely  a  last  stage  of  separation  is  not  settled.  All  the  species 
so  occur,  pectolite  and  datolite  not  so  much  in  the  blowholes  as  in 
veins  and  cavities. 

In  Rocks  and  Ore  Deposits  Due  to  Contact.! 

Somewhat  rare  but  including  some  important  iron  deposits, 
stilbite,  analcite  and  datolite. 

In  Ore  Deposits. 

Not  common  but  including!  Andreasberg,  Harz;  Kongsberg, 
Norway;  Arqueros,  Chili;  Guanajuato,  Mex. ;  and  Republic, 
Washington.  All  but  thomsonite  and  pectolite  are  stated  to  so 
occur. 

Metamorphic  Rocks. 

Stilbite,  chabazite  and  datolite  possibly  more  frequently  than  the 
others  in  gneiss  and  schists,  rarely  in  serpentine. 

*  Brought  here  because  their  mode  of  occurrence  is  like  that  of  the  zeolites  and 
because  the  minerals  which  they  resemble  and  from  which  they  need  to  be  dis- 
tinguished are  chiefly  zeolites. 

t  See  Lindgren,  Mineral  Deposits,  pp.  395,  494,  586. 

\  Ibid.,  p.  395. 

§  Lindgren,  1.  c.  p.  586. 


SILICA   AND    THE  ROCK-FORMING  SILICATES. 


531 


Hot  Springs. 

Stilbite,  chabazite,  and  apophyllite.  The  rare  zeolite  phillipsite 
is  about  the  only  mineral  that  has  been  found  in  deep-sea  dredging. 

THE    OPTICAL    DETERMINATION    OF   ZEOLITES. 

The  zeolites  proper  show  little  or  no  relief  in  balsam  and  are 
usually  colorless,  often  fibrous.  Prehnite,  pectolite  and  datolite 
show  decided  relief. 

Optically  the  minerals  described  may  be  separated  in  two 
divisions  by  their  birefringence.  In  thin  sections  judged  by  inter- 
ference colors. 

BIREFRINGENCE  VERY  Low.     7  —  a  .001  to  .007. 


7—  a 

Character. 

Extinction. 

7 

a 

Analcite 

.OOI 

Isotropic 

1-4 

87 

Chabazite  
Harmotome  
Heulandite  
Stilbite  

•  003 
.005 
.OO6 
.007 

Uniaxial  (—  ) 
Biaxial  (+) 
Biaxial  (+) 
Biaxial  (—  ) 

||  length  =  Yf 
varies 
||  length  =  X 

1.  4 
1.508 

1.505 
1.500 

85 
1-503 
1.498 
1.494 

BIREFRINGENCE  MODERATE  OR  HIGH.     (7  —  0;)  .012  to  .045. 


Natrolite  

.012 

Biaxial  (+) 

||  length  =  Z 

1.488 

1-475 

Thomsonite  

.028 

Biaxial  (+) 

||  length  =  X 

1-525 

1.497 

Prehnite  

•033 

Biaxial  (+) 

||  cleavage  lines 

1.649 

1.616 

Pectolite  

.038 

Biaxial  (+) 

||  length  =  Z 

1.61 

Datolite  

•045 

Biaxial  (—  ) 

|i  c  (nearly)  =  Z 

1.670  1  1.626 

ANALCITE. 

COMPOSITION.  —  NaAl(SiO3)2  +  H2O. 

GENERAL  DESCRIPTION.  —  Small  white  or  colorless  trapezohe- 

FIG.  539.  FIG.  540.  FIG.  541. 


Island  of  Cyclops. 

drons,  Figs.  539,  540,  or  modified  cubes,  Fig.  541 ;  rarely  granular 
or  compact  with  concentric  structure. 

t  Hence  may  be  faster  or  slower  (d=)  than  the  other  ray  according  to  section 
examined. 


532  MINERAL  OGY. 

CRYSTALLIZATION. — Isometric.  The  trapezohedron  n  =  (a:  20, 
:  20)  ;  (21 1),  is  most  frequent  sometimes  modified  by  the  cube  a 
or  dodecahedron  d,  and  in  some  crystals  the  cube  predominates. 

Physical  Characters.— H,,  5  to  5.5.    Sp.  gr.,  2.2  to  2.29. 
LUSTRE,  vitreous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  colorless,  greenish,  red. 

BEFORE  BLOWPIPE,  ETC. — Fuses  easily  and  quietly  to  a  clear, 
colorless  glass.  Yields  water  in  closed  tube.  Gelatinizes  with 
hydrochloric  acid. 

NATROLITE.  —  Needle  Zeolite. 

COMPOSITION.  —  Na2Al(AlO)  (SiO3)3  -f  2H2O. 

GENERAL  DESCRIPTION.  —  Colorless  to  white,  slender,  nearly 
square  prisms,  with  very  flat  pyramids.  Usually  in  radiating  and 
interlacing  clusters  and  bunches.  Also  fibrous  granular  and 
compact. 

CRYSTALLIZATION.  —  Orthorhombic.  Axes  d  :  b  \  c  =  0.979  : 
I  :  0.354*  Angle  of  prism  =  88°  46'. 

Physical  Characters.     H.,  5  to  5.5.     Sp.  gr.,  2.2  to  2.25. 

LUSTRE,  vitreous.  TRANSPARENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  colorless,  white,  yellow,  red.  CLEAVAGE,  prismatic. 

BEFORE  BLOWPIPE,  ETC. — Fuses  very  easily  to  a  colorless  glass. 
In  closed  tube,  yields  water.  Soluble  in  hydrochloric  acid,  with 
gelatinization. 

SIMILAR  SPECIES. — Differs  from  pectolite  in  square  cross-sec- 
tion and  fusion  to  a  clear,  colorless  glass. 

REMARKS. — Occurs  with  other  zeolites  and  with  prehnite,  calcite  and  datolite. 

CHABAZITE. 

COMPOSITION.  — (Ca,  Na2)Al2(SiO3)4  +  6H2O. 

GENERAL  DESCRIPTION. — Simple  rhombohedral  crystals,  almost 
cubic,  also  in  modified  forms  and  twins.  Faces  striated  parallel 
to  edges.  Color,  white,  pale-red  and  yellow. 


SILICA   AND    THE  ROCK-FORMING   SILICATES. 


533 


Physical  Characters.     H.,  4  to  5.     Sp.  gr.,  2.08  to  2.16. 
LUSTRE,  vitreous.  TRANSLUCENT,  transparent. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  red,  yellow.  CLEAVAGE,  parallel  to  the  unit 

rhombohedron. 

CRYSTALLIZATION.  —  Hexagonal.  Scalenohedral  class,  p.  48. 
Axis  c  =  1 .086.  Unit  rhombohedron  p  and  negative  rhombo- 
hedra  e  =  (a  :  co  a  :  a  :  J^);  {1012},  and  /==  (a  :  oo  a  :  a  :  2c)  ; 
{2021}  are  most  common.  Supplement  angles  //=85°  14'; 

^=54°  47'- 

Optically  —  usually,  sometimes  -f  ;  interference  figure  confused. 


FIG.  542. 


FIG.  543. 


FIG.  544- 


FIG.  545- 


BEFORE  BLOWPIPE,  ETC.  - —  Intumesces  and  fuses  to  a  nearly 
white  glass  containing  bubbles.  Yields  water  in  closed  tube. 
Soluble  in  hydrochloric  acid,  leaving  flakes  and  lumps  of  .jelly. 


STILBITE.  —  Desmine. 

COMPOSITION.  — H4(Na2.Ca)  Al2(SiO3)6  +  4H2O. 

GENERAL  DESCRIPTION. — Tab- 
ular crystals,  of  white,  brown  or 
red  color,  pearly  in  lustre  on 
broad  faces  and  frequently  united 
by  these  faces  in  sheaf- like 
groups.  Sometimes  globular  or 
radiated.  Crystals  are  ortho- 
rhombic  in  appearance,  but  really 
complex  monoclinic  twins. 

Physical  Characters.     H.,  3.5  to  4. 
LUSTRE,  vitreous  or  pearly. 
STREAK,  white. 

COLOR,  yellow,  brown,  white,  red. 
CLEAVAGE,  parallel  to  pearly  face. 


Cape  Blomidon,  N.  S. 

Sp.  gr.,  2.09  to  2.2. 
TRANSLUCENT. 
TENACITY,  brittle. 


534 


MINERALOGY. 


BEFORE  BLOWPIPE,  ETC. — Swells  and  exfoliates  in  fan  shapes, 
and  fuses  easily  to  a  white,  opaque  glass.  Yields  water  in  closed 
tube.  Soluble  in  hydrochloric  acid,  with  a  pulverulent  residue. 

HEULANDITE. 

COMPOSITION.  —  H4CaAla(SiO3)6  +  3H2O. 

GENERAL  DESCRIPTION.  —  Monoclinic  crystals,  with  very  bright,  pearly,  cleavage 
surfaces.  The  face  parallel  to  the  cleavage  is  also  bright  pearly,  and  is  less  symmetri- 
cal than  the  corresponding  face  of  stilbite. 

PHYSICAL  CHARACTERS.  —  Transparent  to  translucent.  Lustre,  pearly  and  vitreous. 
Color,  white,  red,  brown.  H.,  3.5-4.  Sp.  gr.  2.18-2.22.  Brittle.  Cleaves  parallel 
to  a  pearly  face. 

BEFORE  BLOWPIPE,  ETC.  —  Exfoliates  and  fuses  easily  to  a  white  enamel.  In  the 
closed  tube  yields  water.  Soluble  in  hydrochloric  acid,  with  a  residue  of  fine  powder. 

HARMOTOME. — H2(K2,Ba)Al2Si6Oi5  +  4H2O.  Occurring  in  crossed  monoclinic 
twins  of  usually  white  color.  H.,  4.5.  Sp.  gr.,  2.44  to  2.50. 

BEFORE  BLOWPIPE,  ETC. — Whitens,  crumbles,  fuses  quietly  at  3.5  to  a  white 
translucent  glass.  Decomposed  by  hydrochloric  acid  without  gelatinizing. 

THOMSONITE.— (Ca.Na2)2Al4(Si04)4  +  5H2O.  Usually  in  radiating  fibers  or 
slender  prismatic  crystals  or  amygdaloidal  with  fibrous  structure  radiating  from 
several  centers  and  of  different  colors. 

BEFORE  BLOWPIPE,  ETC. — Fuses  with  intumescence  at  2  to  a  white  enamel. 
Gelatinizes  with  hydrochloric  acid. 

APOPHYLLITE. 

COMPOSITION. — H14K2Ca8(SiO3)16  +  9H2O,  with  replacement  by 
fluorine. 

GENERAL  DESCRIPTION. — Colorless  and  white  or  pink,  square 
crystals.  Sometimes  flat,  square  plates  or  approximate  cubes ;  at 
other  times  pointed  and  square  to  nearly  cylindrical  in  section. 
Notably  pearly  on  base  or  may  show  in  vertical  direction  a  peculiar 
— fish  eye — internal  opalescence.  Found  occasionally  in  lamellar 
masses. 

CRYSTALLIZATION. — Tetragonal.  Axis  ^=1.252.  Usually  com- 
binations of  unit  pyramid  /,  base  c,  and  second  order  prism  a. 
Supplement  angle  pp  =  76°  ;  cp  =  60°  32'.  Prism  faces  vertically 
striated. 

Physical  Characters.     H.,  4.5  to  5.     Sp.  gr.,  2.3  to  2.4. 
LUSTRE,  vitreous  or  pearly.     TRANSPARENT  to  nearly  opaque. 
STREAK,  white.  TENACITY,  brittle. 

COLOR,  colorless,  white,  pink  or  greenish.      CLEAVAGE,  basal 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        535 


BEFORE  BLOWPIPE,  ETC.  —  Exfoliates  and  fuses  to  a  white  enamel. 
In  closed  tube  yields  water.  In  hydrochloric  acid  forms  flakes 
and  lumps  of  jelly. 


FIG.  546. 


FIG.  547. 


FIG.  548. 


\ 


FIG.  549. 


PECTOLITE. 


COMPOSITION.  — HNaCa2(SiO3)3. 

GENERAL  DESCRIPTION.  —  White  or  gray  radiating  needles  and  fibers  of  all  lengths 
up  to  one  yard.  Also  in  tough  compact  masses  and  rarely  in  monoclinic  crystals. 

PHYSICAL  CHARACTERS.  —  Translucent  to  opaque.  Lustre,  vitreous  or  silky. 
Color,  white  or  gray.  Streak,  white.  H.,  5.  Sp.  gr.,  2.68  to  2.78.  Brittle. 

BEFORE  BLOWPIPE,  ETC.  —  Fuses  easily  to  a  white  enamel-  Yields  water  in 
closed  tube.  Gelatinizes  with  hydrochloric  acid. 

REMARKS. — Occurs  with  zeolites,  prehnite,  etc.,  in  cavities  and  seams  of  basic 
eruptive  rocks. 

PREHNITE. 

COMPOSITION.  —  H2Ca2Al2(SiO4)3. 

GENERAL  DESCRIPTION.  —  A  green  to  grayish-white  vitreous 
mineral.  Sheaf-like  groups  of  tabular  crystals,  united  by  the  basal 
planes.  Sometimes  barrel -shaped  crystals  and  frequently  reniform 
or  botryoidal  crusts,  Fig.'  270,  with  crystalline  surface. 

Physical  Characters.     H.,  6  to  6.5.     Sp.  gr.,  2.8  to  2.9$. 
LUSTRE,  vitreous.  TRANSLUCENT. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  light  to  dark  green  or  grayish-white.   CLEAVAGE,  basal. 

BEFORE  BLOWPIPE,  ETC. — Easily  fusible  to  a  whitish  glass  con- 
taining bubbles.  In  closed  tube  yields  a  little  water.  Soluble  in 
hydrochloric  acid,  and  after  fusion  is  soluble  with  a  gelatinous 
residue. 


536 


MINERALOGY. 


SIMILAR  SPECIES.— Resembles  calamine  or  green  smithsonite 
somewhat,  but  is  more  easily  fused,  and  does  not  gelatinize  unless 

previously  ignited. 

DATOLITE. 

COMPOSITION.— Ca(B.OH)Si04. 

GENERAL  DESCRIPTION. — Highly  modified,  glassy,  monoclinic 
crystals  often  lining  a  cavity  in  a  basic  rock.  Usually  colorless, 
but  also  white  or  greenish.  Also  in  compact,  dull,  white  or  pink 
masses,  resembling  unglazed  porcelain. 


FIG.  550. 


FIG.  551. 


FIG.  552. 


Bergen  Hill,  N.  J. 


Lake  Superior. 


CRYSTALLIZATION.  —  Monoclinic.  /?=89°  51'.  Axes  a\b\ 
c  *=.  0.634  :  i  :  1.266.  Prominent  forms  are  the  pinacoids  a  and 
ct  the  unit  prism  m,  negative  unit  pyramid  ]>,  unit  clino-dome 
d,  clino-prism  /=  (20,  :  b  :  oo^),  {120}  ;  and  positive  hemi-pyramid 
r=  (a  :  b  :  Jr),  {112}.  Supplement  angles  are  mm  =  64°  47'  ; 
//=;6°  29';  J5J5=59°5';  dd=  103°  23'. 

Physical  Characters.     H.,  5  to- 5. 5.     Sp.  gr.,  2.9  to  3. 

LUSTRE,  vitreous.  TRANSLUCENT  to  nearly  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  colorless,  white,  greenish. 

BEFORE  BLOWPIPE,  ETC. — In  forceps  or  on  charcoal  fuses  easily 
to  a  colorless  glass,  and  if  mixed  with  a  flux  of  acid  potassium 
sulphate  and  calcium  fluoride  and  a  little  water  it  will  color  flame 
green.  In  closed  tube  yields  water  at  a  high  heat.  Soluble  in 
hydrochloric  acid,  with  gelatinization. 

SIMILAR  SPECIES.  —  Differs  from  the  zeolites  in  crystalline  form 
and  flame  and  from  colemanite  by  gelatinization. 


SILICA    AND    THE  ROCK-FORMING   SILICATES.         537 

THE  MICA   GROUP. 

The  minerals  described  are: 

Muscovite                  H2(K.Na)Al3(SiO4)3  Monoclinic 

Biotite                         (H.K)2(Mg.Fe)2Al2(SiO4)3  Monoclinic 

Phlogopite                  R3Mg3Al(SiO4)3  Monoclinic 

Margarite                    I^CaAUSiaOw  Monoclinic 


The  micas  are  characterized  by  the  very  perfect  basal  cleavage, 
the  cleavages  are  usually  elastic  but  in  margarite  slightly  brittle. 
They  occur  in  lamellar  and  scaly  masses  and  sometimes  in  mono- 
clinic  crystals  easily  mistaken  for  hexagonal  or  orthorhombic. 

FORMATION   AND   OCCURRENCE   OF   THE   MICAS. 

Separation  from  Magma. 

Biotite  very  common,  disseminated  in  granite,  syenite,  diorite, 
trachyte,  andesite,  gabbro,  peridotite,  the  best  crystals  are  in 
volcanic  ejecta,  large  plates  sometimes  occur  in  granite. 

Muscovite.  —  Alone  or  more  frequently  with  biotite  as  an  im- 
portant constituent  of  many  granites  and  some  quartz  porphyries 
but  not  in  recent  volcanic  rocks. 

Phlogopite.  —  In  some  peridotites  and  leucite  lavas. 

In  Pegmatites. 

Muscovite,  phlogopite,  lepidolite. 
Contact  Metamorphism. 

Biotite,  muscovite  common,  phlogopite  in  dolomitic  limestone. 

Margarite  in  rocks  high  in  alumina  as  at  Crugers  Point,  N.  Y., 
with  staurolite  and  tourmaline. 

Metamorphic  Rocks. 

Biotite  in  gneisses  and  schists  in  large  amounts. 

Muscovite  is  very  common  in  mica  schists  and  gneiss.  The 
secondary  variety  sericite,  formed  by  the  alteration  of  feld- 
spars, quartz  porphyries,  and  various  silicates  carrying  aluminum, 
often  forms  schists,  frequently  mistaken  for  talcose  schist. 

Paragonite,  forming  schists  in  Switzerland  and  Tyrol. 

Phlogopite  in  granular  limestones  and  serpentine. 

Margarite  is  invariably  associated  with  corundum  and  emery  as  if 
formed  from  them. 


538 


MINERALOGY. 


OPTICAL   DETERMINATION   OF   THE   MICAS. 

The  tests  are  on  basal  or  transverse  sections. 

Transverse  Sections. 

Often  lath-like  with  parallel  cleavage  cracks.  When  the  plane 
of  the  lower  nicol  is  parallel  to  these  cracks  there  is : 

With  one  nicol. — Maximum  absorption  and  pleochroism.  Indices 
ranging  1.57  to  1.64,  but  overlapping  so  as  not  to  be  distinctive. 

With  crossed  nicols. — Extinction  except  with  margarite  and  un- 
usual biotite,  which  have  small  extinction  angles. 

Basal  Sections. 

Often  scales  or  hexagonal  plates,  always  approximately  per- 
pendicular to  the  acute  bisectrix  X. 

With  convergent  light  are  all  biaxial  (-).  Axial  angle  varying 
widely. 

With  conical  point. — Percussion  figure,  p.  215,  the  most  promi- 
nent line  parallel  (oio).  If  the  line  connecting  the  axes  of  the 
interference  figure  is  at  right  angles  to  this  the  mica  is  said  to  be 
of  the  first  order,  Fig.  553,  if  parallel,  of  the  second  order  Fig.  554. 


553 


554 


First  Order. 


Second  Order. 


The  birefringence  in  the  two  sections  is  notably  different  (see 
7  —  a  and  7  —  j3). 


Transverse  Section. 

Basal  Section. 

V  —  a 

Extinction. 

Pleochroism 

y  —  ft 

Order. 

2Et 

Biotite  
Muscovite  .  . 
Paragonite.  . 
Phlogopite  .  . 
Margarite.  .  . 

.033  to  .060 
.033  to  .049 
Large 
.044 
.009 

o°  (rarely  10°) 

0° 
0° 
0° 

6°  + 

Strong 
None 
None 
Moderate 
None 

o 
.005  to  .008 
Small 
o 
Small 

Second* 
First 
First 
Second 

o°  to  12° 
60°  to  80° 
70?° 
o°  to  30° 

76°  tO  120° 

*  Except  anomite. 

t  Exceptional  biotites  have  2E  60°  to  70°  and  exceptional  muscovites  have  small 
angles. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.         539 

MUSCOVITE.  —  Potash  Mica,  White  Mica,  Isinglass. 

COMPOSITION.  —  H2(K.Na)Al3(SiO4)3,*with  some  replacement  by 
Mg  or  Fe. 

GENERAL  DESCRIPTION.  —  Disseminated  six-sided  scales  and 
rough  crystals,  which  cleave  with  great  ease  into  thin,  elastic, 
transparent  leaves.  Also  in  masses  of  coarse  or  fine  scales  some- 
times grouped  in  globular,  stellate  and  plumose  forms.  Usually 
transparent  and  pale  gray  in  color,  and  with  pearly  lustre  on  the 
cleavage  surfaces. 

CRYSTALLIZATION.  —  Monoclinic.  ft  =  89°  54'.  Prism  angle 
=  59°  48'.  Crystals  usually  rhombic  or  hexagonal  in  section, 
with  rough  faces,  and  usually  tapering.  Sometimes  very  large, 
several  feet  across.  Cleavage  is  approximately  at  right  angles  to 
the  prism. 

FIG.  555  FIG.  556 


Physical  Characters.     H.,  2  to  2.5.     Sp.  gr.,  2.76  to  3. 

LUSTRE,  vitreous,  pearly  on  cleavage.     TRANSPARENT  in  laminae. 
STREAK,  white.  TENACITY,  elastic. 

COLOR,  gray,  brown,  green,  yellow,  violet,  red,  black. 
CLEAVAGE,  basal,  eminent. 

BEFORE  BLOWPIPE,  ETC. — Fuses  only  on  thin  edges  to  a  yellow- 
ish glass.  Insoluble  in  acids. 

SIMILAR  SPECIES. — Differs  from  talc  or  gypsum  in  being  elastic, 
Is  usually  lighter  colored  than  biotite. 

VARIETIES: 

Fuchsite  is  a  green  muscovite  containing  chromium. 

Sericite  is  secondary  muscovite  formed  in  the  weathering  and  alteration  of  feldspars 
and  other  silicates  as  nephelite,  scapolite  and  andalusite.  It  occurs  in  fine  white 
scaly  or  silky  aggregates  often  called  talc  schist  and  also  often  embedded  in  the 
cloudy  portion  of  the  feldspar.  Damourite,  margarite,  pinite,  gieseckite  are  essentially 
the  same  material. 

REMARKS. — The  occurrence,  p.  537,  and  uses  p.  481  have  been  described.  The 
most  productive  mica  mines  of  the  United  States  are  in  Mitchell,  Yancey,  Jackson 
and  Macon  Counties,  S.  C.,  and  Groton,  N.  H.  Other  large  deposits  exist  at  Grafton, 
N.  H.;  Las  Vegas  and  Cribbensville,  N.  M.,  and  Deadwood  and  the  Black  Hills,  S. 


540  MINER  A  LO  G  Y. 

D.,  many  of  which  are  intermittently  mined.  Also  in  Nevada,  California,  Colorado 
and  Pennsylvania  in  quantity  and  quality  fit  for  use.  Large  quantities  of  mica  are 
annually  imported  from  India. 

PARAGONITE. — H2NaAl2(SiC»4)3  or  sodium  muscovite,  occurring  in  massive 
scaly  aggregates  similar  to  sericite  but  not  known  as  a  primary  mineral.  It  consti- 
tutes the  mass  of  a  rock  at  Mt.  Campione,  Switzerland,  containing  staurolite  and 
cyanite  and  a  soapstone-like  mass  with  actinolite  at  Pfitschthal  and  Zillerthal,  Tyrol. 

BIOTITE. — Black  Mica,  Magnesium  Mica. 

COMPOSITION. — An  orthosilicate  approximating  (H.K)2(Mg.Fe)2~ 
Al2(Si04)3. 

GENERAL  DESCRIPTION. — The  most  common  of  the  micas. 
Accompanies  muscovite  in  granitic  rocks  and  schists,  but  is  usually 
dark  green  to  black  in  color  and  in  comparatively  small  scales. 
Also  as  black,  green  and  red  crystals  at  Vesuvius.  It  cleaves  into 
thin,  elastic  leaves. 

CRYSTALLIZATION. — Monoclinic.  0  =  90°.  a  :  b  :  c  =  0.577  : 
i  :  3.274.  Habit  tabular,  Fig.  555.  mm  supplement  angle  60°. 

Physical  Characters.     H.,  2.5  to  3      Sp.  gr.,  2.7  to  3.1. 

LUSTRE,  pearly,  vitreous,  submetallic.   TRANSPARENT  to  opaque. 
STREAK,  white.  TENACITY,  tough  and  elastic. 

COLOR,  commonly  black  to  green.   CLEAVAGE,  basal,  eminent. 

BEFORE  BLOWPIPE,  ETC.     Whitens  and  fuses  on   thin  edgos. 
Decomposed    by  boiling    sulphuric    acid, 
FIG.  557  with  separation  of  scales  of  silica. 

REMARKS. — Occurs  as  described  on  p.  537.  It 
alters  much  more  readily  than  muscovite,  epidote,  or 
hydrous  micas.  Prominent  localities  are  Vesuvius, 
Lake  Baikal,  Greenwood  Furnace,  N.  Y.,  Pikes  Peak. 
Col.,  Butte,  Mont. 

PHLOGOPITE.  —  Amber  Mica,  Bronze  Mica. 

COMPOSITION.  —  R3Mg3Al(SiO4)3,  where  R  =  H,K,MgF. 

GENERAL  DESCRIPTION.  —  Large  and  small,  brownish-red  to 
nearly  black  crystals.  Usually  rough,  tapering,  six-sided  prisms. 
Thin  plates  sometimes  show  a  six-rayed  star  by  transmitted  light. 

Optically  — .  Axial  plane  parallel  to  b,  that  is  parallel  to  the 
principal  line  of  the  percussion  figure.  Axial  angle  small,  but 
varying  in  the  same  specimen.  Pleochroic  in  colored  varieties. 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        541 

Physical  Characters.    H.,  2.5  to  3.     Sp.  gr.,  2.78  to  2.85. 
LUSTRE,  pearly  or  submetallic.     TRANSPARENT  to  translucent. 
STREAK,  white.  TENACITY,  tough  and  elastic. 

COLOR,  yellowish-brown,  brownish-red,  green,  colorless. 
CLEAVAGE,  basal  eminent. 

BEFORE  BLOWPIPE,  ETC. — Whitens  and  fuses  on  thin  edges.  In 
closed  tube  yields  water.  Soluble  in  sulphuric  acid  with  separa- 
tion of  scales  of  silica. 

REMARKS. — Occurs  in  enormous  crystals  in  Ontario  and  Quebec,  and  in  various 
localities  through  New  York  and  New  Jersey. 

MARGARITE. 

COMPOSITION. — H2CaAl4Si2Oi2  =  Silica  30.2,  alumina  51.3,  lime  14.0,  water 
4.5  =  100. 

GENERAL  DESCRIPTION. — Gray  to  pink  micaceous  material  with  pearly  lustre, 
incrusting  corundum  or  associated  with  it.  H.,  3.5  to  4.5.  Sp  gr.,  2.99  to  3.08. 

BEFORE  BLOWPIPE,  ETC. — Whitens  and  fuses  at  4.5.  Yields  water  in  closed  tube. 
Slowly  decomposed  in  hydrochloric  acid. 

REMARKS. — Found  in  this  country  with  corundum  at  Chester,  Mass. ;  Unionville, 
Pa.;  Crugers  Point,  N.  Y.;  Gainesville,  Ga.;  Dudley ville,  Ala.  Foreign  occurrences 
are  Naxos  and  Gumuch-Dagh,  Asia  Minor;  Sterzing,  Tyrol,  etc. 

THE   CHLORITE   GROUP. 

The  species  described  are: 

Clinochlore  \H8(Mg,Fe)  lAhSbOw  Monoclinic 

Penninite  J 

Prochlorite  H4o(Fe,Mo)23AIi4Sii3O2o  Monoclinic 

Species  or  doubtful  species  elsewhere  described   are  chamosite, 
ihuringite  and  berthierine,  p.  276. 

Many  other  names  have  been  given,  the  chlorites  being  probably 
isomorphous  mixtures  of  undetermined  end  members. 

Tschermak  assumed  an  isomorphous  series  analogous  to  the  plagioclase  series 
with  serpentine  (Sp),  H4(Mg.Fe)3Si2O9,  at  one  end  and  a  chlorite  from  Chester,  Mass., 
Amesite  (At),  H4(Mg.Fe)2Al2Si2O9,  as  the  other.  On  this  theory  the  distinctly 
crystallized  species  clinochlore  and  penninite  are  SpAt,  the  species  prochlorite  is 
SpaAtn  and  the  species  corundophilite  SpAU. 

A  number  of  dark  green  chlorite-like  substances  occurring  in 
fine  scales  and  fibres  and  not  distinguishable  from  one  another 
microscopically  are  given  names  on  the  basis  of  analyses  but  are 
in  general  simply  described  as  chlorites  or  leptochlorites.  Delessite 
is  a  type. 


542 


MINERALOGY. 


FORMATION   AND   OCCURRENCE   OF   CHLORITES. 

In  Igneous  Rocks. 

They  are  never  primary  in  igneous  rock  but  very  common  as 
secondary  minerals  not  only  as  the  green  unidentified  pigment 
called  viridite  but  as  irregular  scaly  aggregates  and  pseudomorphs 
formed  from  biotite,  amphibole,  pyroxene,  garnet,  or  less  directly 
from  feldspars  and  ferromagnesian  minerals  combined. 

In  Metamorphic  Rocks. 

Very  widely  distributed  and  very  difficult  usually  to  distinguish 
from  one  another.  Sometimes  dominant  forming  chlorite  schists, 
or  in  other  schists,  sometimes  forming  veins  in  serpentine,  often 
with  magnetite. 

OPTICAL   DETERMINATION   OF   CHLORITES. 

The  microscopic  varieties  are  optically  indistinguishable,  the 
coarse  may  in  part  be  distinguished  from  each  other. 

Characters  in  Common. 

In  transverse  section. 

Color  usually  green,  occasionally  red  (Cr). 

Relief  slight  in  balsam.     7  =  i  .57  to  1 .59. 

Pleochroism  marked  in  greens  and  yellows. 
In  basal  section. 

Pleochroism  not  observable. 

Interference  colors  none  or  faint. 

Differential  Characters. 


Extinction 
with  Cleav- 
age.    Z  to  c 

Axial 

A°f" 

Interference  Colors 
(Transverse  Section) 
7  —  a. 

Interference 
Figure. 

Clinochlore  
Penninite  

Prochlorite  

2°  to  7° 

0° 

o°  + 

12°  tO  90° 

o°  + 
o°  to  30° 

.01  like  quartz 
.001  to  .003  nearly  black  or 
anomalous  indigo  blue 

Biaxial  (+) 
Uniaxial  (db) 

Biaxial  (+) 

CLINOCHLORE. 

COMPOSITION. — H8(Mg.Fe)5Al2Si3Oi8. 

GENERAL  DESCRIPTION. — Green,  white  and  rose-red  crystals  with  cleavage  like 
mica,  the  cleavage  plates  however  being  only  slightly  elastic.  Also  masses  made 
up  of  coarse  or  fine  scales  and  earthy.  H.,  2  to  2.5.  Sp.  gr.,  2.65  to  2.78. 

CRYSTALLIZATION.— Monoclinic.  Pseudohexagonal.  Crystals  usually  six-sided 
plates,  or  sometimes  with  rhombohedral  habit. 


SILICA   AND    THE  ROCK-FORMING   SILICATES.        543 

BEFORE  BLOWPIPE,  ETC.  —  Whitens  and  fuses  with  difficulty  to  a  grayish  black 
glass.  In  closed  tube  yields  water  at  a  high  heat.  Soluble  in  sulphuric  acid,  only 
slightly  so  in  hydrochloric  acid. 

REMARKS.  —  Found  in  green  chlorite  schist  at  Achmatowsk,  Urals,  and  Zillerthal, 
Tyrol.  In  serpentine  at  Westchester,  Penn.  Rose  red  (kotschubeile)  in  California 
and  Urals.  White  (leuchtenbergite)  in  Traversella,  etc. 

PENNINITE. 

COMPOSITION.  —  Like  clinochlore. 

GENERAL  DESCRIPTION.  —  Like  clinochlore  but  crystals  thick  pseudorhombodehral 
or  tapering. 

BEFORE  BLOWPIPE.  —  Like  clinochlore. 

REMARKS.  —  The  differences  are  chiefly  optical  (see  p.  542)  and  in  habit  of  crystals. 
Found  in  Zermatt,  Switzerland;  Zillerthal,  Tyrol;  Ala,  Piedmont;  Texas,  Penn.,  as 
cherry  red  kammererite. 

PROCHLORITE. 

COMPOSITION.  —  H4o(Fe.Mg)23Ali4Sii3O9o. 

GENERAL  DESCRIPTION.  —  Dark-green  masses,  composed  of  coarse  to  very  fine 
scales.  Also  tabular  and  sometimes  twisted  six-sided  crystals,  which  easily  cleave 
into  thin  plates  which  are  not  elastic.  H.,  i  to  2.  Sp.  gr.,  2.78  to  2.96. 

BEFORE  BLOWPIPE,  ETC.  —  Whitens  and  fuses  to  a  nearly  black  glass.  In  closed 
tube  yields  water.  Soluble  in  sulphuric  acid. 

REMARKS.  —  Found  massive  in  Montgomery  Co.,  N.  C.,  and  in  the  tin  veins  of 
Cornwall.  Other  localities  are  St.  Gothard  on  adularia;  Traversella,  Piedmont; 
Zillerthal,  Tyrol;  Washington,  D.  C. 

DELESSITE,  a  dark-green  massive  mineral  of  scaly  or  short  fibrous  appearance. 
H.,  2.5.  Sp.  gr.,  2.9.  It  yields  water  in  the  closed  tube  and  is  decomposed  by  HC1 
with  separation  of  silica.  Found  in  cavities  of  amygdaloidal  eruptive  rocks. 

THE  HYDROUS  SILICATES  OF  MAGNESIUM. 

The  species  described  are  : 


Serpentine 

Talc  •    H2Mg3(SiO3)4  Monoclinic 

Sepiolite  H4Mg2Si3Oio 

FORMATION   AND    OCCURRENCE. 

Both  are  secondary  minerals  chiefly  formed,  it  is  believed,  by 
the  alteration  (possibly  by  carbonated  water)  of  magnesian  silicates 
such  as  chrysolite,  enstatite,  hypersthene,  anthophyllite  and  tremolite, 
but  also  by  the  action  of  magnesian  waters  on  non  magnesian 
silicates  such  as  feldspar. 

Secondary  in  Igneous  Rocks. 

Serpentine  forms  as  a  rock  from  peridotite,  according  to  Wein- 
schenck,*  other  rocks  such  as  pyroxenite  "never  turn  to  serpen- 
tine." _  V" 

*  "  Petrographic  Methods,"  315  (Weinschenck-Clark). 


544  MINER ALOG  Y. 

Serpentine  forms  as  pseudomorphs  in  rocks  containing  chrysolite, 
etc.,  sometimes  after  the  parent  mineral,  sometimes  after  a  mineral 
which  it  has  displaced. 

Talc  may  form  as  a  rock  from  peridot! te.*     Soapstone  is  probably 
altered  eruptive  rock. 
In  Metamorphic  Rocks. 

Serpentine  in  layers  between  gneiss,  granulite,  limestone,  talc 
and  chlorite  schist. 

Talc  is  common  in  chloritic  schists,  serpentine,  dolomite,  etc. 
The  talc  beds  of  St.  Lawrence  Co.,  N.  Y.,  are  regarded  as  secondary 
alterations  of  tremolite  or  enstatite  in  schistose  limestone.     For 
instance  Clarke  gives  t 
2Mg2SiO4  +  2H2O  +  C02  =  H4Mg3Si2O9  +  MgCO3 

(Chrysolite)  (Serpentine)         (Magnesite) 

CaMg3(Si03)4  +  H20  +  C02  =  H2Mg2(SiO5)4  +  CaCO3 

(Tremolite)  (Talc)  (Calcite) 

THE   OPTICAL   DETERMINATION. 

Serpentine  and  talc  in  thin  sections  are  essentially  colorless,  non- 
pleochroic  and  with  little  relief  (7  1.51  to  1.59).  Both  are  biaxial 
and  the  lammellae  of  antigorite  and  talc  may  show  interference 
figures  respectively  (+)  and  (  — ).  The  elongation  of  chrysotile 
fibres  is  (+).  Antigorite  laths  show  as  "lattice  structure," 
chrysotile  fibres  as  "net  or  mesh  structure."  The  minerals  differ 
optically  chiefly  in  birefringence.  7  —  a  in  serpentine  is  .on  to 
.013,  giving  colors  in  thin  sections  in  middle  and  end  of  first  order. 
In  talc  7  —  a  is  .038  to  .043,  giving  bright  third  order  colors  like 
muscovite.  Indeed  sericite  (muscovite)  and  talc  are  not  dis- 
tinguishable by  optical  tests. 

SERPENTINE. 

COMPOSITION.— H4Mg3Si2O9,  with  replacement  by  Fe. 

GENERAL  DESCRIPTION. — Fine  granular  masses  or  microscop- 
ically fibrous.  Also  foliated  and  coarse  or  fine  fibrous.  Color, 
green,  yellow  or  black,  and  usually  of  several  tints  dotted,  striped 
and  clouded.  Very  feeble,  somewhat  greasy  lustre  and  greasy 
feel.  Crystals  unknown. 

*  Ibid.,  317,  by  "intense  chemical  processes"  sometimes  near  acid  eruptives. 
t  Bull.  U.  S.  Geol.  Surv.  491,  p.  575  and  578. 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        545 

Physical  Characters.     H.,  2.5  to  4.,  Sp.  gr.,  2.5  to  2.65. 
LUSTRE,  greasy,  waxy  or  silky.  TRANSLUCENT  to  opaque. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  green  to  yellow,  brown,  red,  black,  variegated. 

BEFORE  BLOWPIPE,  ETC. — Fuses  on  edges.  In  closed  tube, 
I  yields  water.  In  cobalt  solution  becomes  pink.  Soluble  in  hy- 
I  drochloric  acid,  with  a  residue. 

VARIETIES  : 

Serpentine  Rock. — Containing  the  three  varieties  below  with 
unaltered  chrysolite,  pyroxene,  etc.,  and  by-products  chromite, 
magnetite,  magnesite,  sometimes  garnierite. 

Antigorite. — Lamellar  or  flaky  deep  green  material  or  lath-like 
crystals  in  seams  and  crevices  of  serpentine  rock. 

Chrysotile. — Seams  and  crevices  in  the  chrysolite  fill  with  fibres 
perpendicular  to  their  sides  and  later  the  compact  serpentine  fills 
in  between. 

Massive  or  Compact  Serpentine. — Dense  aggregates  making  up 
the  ground  mass  of  most  occurrences. 

REMARKS. — Chrysotile  in  commercial  quantities  occurs  in  Vermont  and  Arizona; 
the  great  source  however  is  the  Thetford  region,  Quebec,  Canada.  Massive  serpen- 
tine or  verd  antique  marble  is  obtained  at  Milford,  Conn.  Many  localities  such  as 
Newburyport,  Mass.;  Montville,  N.  J.;  Texas,  and  West  Chester,  Penn.,  yield 
serpentine  of  ornamental  quality.  Well-known  foreign  localities  are  Falun,  Sweden; 
Portsay,  Aberdeen;  the  Lizard  Cornwall,  New  Zealand  (Bowenite). 

TALC.— Steatite,  Soapstone. 

COMPOSITION. — H2M  g3(SiO3)4. 

GENERAL  DESCRIPTION. — A  soft,  soapy  material,  occurring  foli- 
ated, massive,  and  fibrous,  with  somewhat  varying  hardness.  Usu- 
ally white,  greenish  or  gray  in  color.  Crystals  almost  un- 
known. 

Physical   Characters.     H.,  i  to  4.     Sp.  gr.,  2.55  to  2.87. 
LUSTRE,  pearly  or  wax-like.  TRANSLUCENT. 

STREAK,  white.  TENACITY,  sectile. 

COLOR,  white,  greenish,  gray,  brown,  red. 
CLEAVAGE,  into  non-elastic  plates.  FEEL,  greasy. 

36 


546  MINERALOGY. 

BEFORE  BLOWPIPE,  ETC. — Splits  and  fuses  on  thin  edges  to  white 
enamel.  With  cobalt  solution,  becomes  pale  pink.  Insoluble  in 
acid. 

VARIETIES. 

Foliated  Talc. — H  =  I.  White  or  green  in  color.  Cleavable 
into  non-elastic  plates. 

Soapstone  or  Steatite. — Coarse  or  fine,  gray  to  green,  granular 
masses.  H.,  1.5  to  2.5. 

French  Chalk. — Soft,  compact  masses,  which  will  mark  cloth. 

Agolite. — Fibrous  masses  of  H.  3  to  4. 

Rensselaerite. — Wax-like  masses.  H.,  3  to  4.  Pseudomorphous 
after  pyroxene. 

SIMILAR  SPECIES. — Softer  than  micas  or  brucite  or  gypsum. 
Further  differentiated  by  greater  infusibility,  greasy  feel,  and  the 
flesh-color  obtained  with  cobalt  solution. 

REMARKS. — Much  of  the  so-called  talc  schist  has  proved  to  be  sericite  (or  secon- 
dary muscovite)  in  scaly  aggregates  harder  than  talc  but  undistinguishable  optically. 
An  immense  deposit  of  fibrous  talc  at  Gouverneur  and  Edwards,  N.  Y.,  is  mined, 
and  the  total  output  is  ground  for  use  in  paper-making,  etc.  Large  soapstone 
quarries  are  worked  at  Francestown,  N.  H.,  Chester,  Saxon's  River,  Cambridgeport 
and  Perkinsville,  Vt.,  Cooptown,  Md.,  and  Webster,  N.  C.  Massachusetts,  New 
Jersey,  Pennsylvania,  Virginia  and  Georgia  are  also  producing  states. 

SEPIOLITE.— Meerschaum. 

COMPOSITION. — H4Mg2Si3O10. 
GENERAL  DESCRIPTION. — Soft  compact  white,  earthy  to    clay- 
like  masses,  of  very  light  weight.     Rarely  fibrous. 

Physical  Characters.     H.,  2  to  2.5.     Sp.  gr.,  i  to  2. 
LUSTRE,  dull.  '   OPAQUE. 

STREAK,  white.  TENACITY,  brittle. 

COLOR,  white,  gray,  rarely  bluish-green.        FEEL,  smooth. 

BEFORE  BLOWPIPE,  ETC.— Blackens,  yields  odor  of  burning  and 
fuses  on  thin  edges.  In  closed  tube  yields  water.  With  cobalt 
solution  becomes  pink.  In  hydrochloric  acid  gelatinizes. 

>SIMILAR  SPECIES.— Resembles  chalk,  kaolinite,  etc.,  but  is 
characterized  by  lightness  and  gelatinization  with  acids. 

REMARKS.— Possibly  formed  from  Magnesite.  The  name  "meershaum"  refers  to 
to  the  fact  that  it  will  float  on  water  when  dry.  Most  of  the  material  used  for  pipes  is 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        547 

obtained  from  Turkey.     It  occurs  in  large  amount  in  Spain,  and  in  smaller  quantities 
in  Greece,  Morocco  and  Moravia.     There  are  no  productive  American  localities. 

USES. — As  material  for  costly  tobacco  pipes.     In  Spain  it  is  a 
building  stone.     In  Algeria  it  is  used  as  a  soap. 

THE  HYDROUS   SILICATES   OF  ALUMINUM. 

The  species  described  are : 

T  Kaolinite  H4Al2Si2O9 

Well  characterized  |  Pyrophyllite  HAl(SiO3)2 

.,,  R alloy site  H4Al2Si2O9  +  H2O 

Poorly  characterized         •<  Allophane  Al2SiO6  +  SH2O 

Montmorillonite  H2Al2(SiC>3)4  +  nH2O 

FORMATION  AND   OCCURRENCE. 

Residual  and  Sedimentary  Clays. 

The  great  aluminum  silicates,  especially  the  feldspars,  nephelite, 
and  wernerite,  by  weathering,  tend  to  form  hydrous  silicates  of 
aluminum  as  residual  products.  These  consist  in  part  probably 
of  the  definite  silicate  kaolinite*  chemically  equivalent  to  serpen- 
tine but  largely  of  colloidal  residues,  "gels,"  less  definitely  recog- 
nizable and  hardly  to  be  called  true  minerals.  The  deposits 
known  as  CLAYS  contain  also  free  quartz  and  varying  amounts 
of  many  other  species.  The  clays  may  be  "  residual "  resulting 
from  decay  in  place  as  with  the  china  clays  of  Meissen,  Saxony,  and 
Cornwall,  England,  or  they  may  have  been  transported  by  water, 
ice  or  wind  and  redeposited  as  "  sedimentary  "  clays.  The  original 
rocks  from  which  they  formed  may  be  of  almost  any  class,  granites 
syenites,  pegmatites  and  even  basic  rocks;  gneiss,  limestones, 
shales.  Plasticity  in  clays  appears  to  be  dependent  on  the  col- 
loidal matter  present  whether  silicic  acid,  alumina,  iron  oxide  or 
organic. f 

KAOLINITE.— Kaolin,  China  Clay. 

COMPOSITION.— H4Al2Si2O9. 

GENERAL  DESCRIPTION. — Compact  and  clay-like  or  loose  and 
mealy  masses  of  pure  white,  or  tinted  by  impurities  composed  of 

*  The  usual  formula  given  is 

2KAlSi308  +  2H2O  +  CO2  =  H4Al2Si209  +  K2CO3  +  4SiO2. 

Orthoclase  Kaolinite 

t  See  N.  B.  Davis,  Trans.  Am.  Inst.  Min.  Engs.,  Feb.,  1915. 


548 


MINERALOGY. 


extremely  minute  scales  and  plates.     Rarely  crystallized  in  small 
rhombic  or  six-sided  plates  optically  monoclinic. 

Physical  Characters.     H.,  2  to  2.5.    Sp.  gr.,  2.6  to  2.63. 

LUSTRE,  dull  or  pearly.  OPAQUE  or  translucent. 

STREAK,  white  or  yellowish.  TENACITY,  brittle. 

COLOR,  white,  yellow,  brown,  red  and  blue. 

It  is  stated  that  the  cloudy  effects  in  feldspars  are  due  to  sericite 
and  not  kaolin  which  is  rarely  observed  in  thin  sections.*  Kaolinite 
should  show  no  relief  (index  1 .55)  in  balsam  and  low  interference 
colors  (7  —  a  =  .007). 

BEFORE  BLOWPIPE,  ETC. — Infusible.  Yields  water  in  closed 
tube.  With  cobalt  solution,  becomes  deep  blue.  Decomposed 
by  sulphuric  acid,  but  is  insoluble  in  nitric  or  hydrochloric  acids. 

REMARKS. — Kaolinite  in  crystalline  scales  occurs  at  the  National  Bell  Mine,  Silver- 
ton,  Col.,  and  at  Tamaqua,  Penn.  Kaolinite  is  mined  at  Okahumka,  Lake  County, 
Florida,  at  Sylva,  Dilsboro  and  Webster,  N.  C.,  and  at  several  places  in  New  Castle 
County,  Del.,  and  Chester  and  Delaware  Counties,  Pa.  Kaolin  of  poorer  quality 
is  obtained  in  Ohio  and  New  Jersey,  and  many  other  deposits  are  known  throughout 
the  Atlantic  States. 

FIG.  558. 


Pyrophyllite,  Lincoln  Co.,  Ga.     N.  Y.  State  Museum. 

FYROPHYLLITE.— Pencil  Stone. 

COMPOSITION.— HAl(SiO3)2. 

GENERAL  DESCRIPTION.— Radiated  foliae  or  fibres  and  compact  masses  of  soapy 
feeling  and  soft  and  smooth  like  talc. 

*  Weinschenck-Clark,  "  Petrographic  Methods,"  p.  318. 


SILICA   AND    THE  ROCK-FORMING  SILICATES.        549 

white,  greenish,  brownish  or  yellow.  Streak,  white.  H.,  I  to  2.  Sp.  gr.,  2.8  to  2.9. 
Flexible. 

BEFORE  BLOWPIPE,  ETC. — Whitens  and  fuses  on  the  edges,  and  often  swells  and 
spreads  like  a  fan.  In  closed  tube  yields  water.  Partially  soluble  in  sulphuric  acid. 

REMARKS. — Occurs  in  beds  with  schists  as  compact  material  at  Deep  River,  N.  C.. 
and  as  foliated  material,  often  radiated,  in  Lincoln  Co.,  Ga.;  Ouro  Preto,  Brazil, 
Often  with  cyanite. 

USES. — Extensively  manufactured  into  slate  pencils,  foot  warmers  and  other 
uses  of  "soapstone." 

HALLO YSITE.— Probably  H4Al2Si2O9  +  H2O  (Le  Chatelier).  Amorphous  clay- 
like  white  or  yellowish  material.  H.,  i  to  2.  Sp.  gr  ,  2.0  to  2.2. 

BEFORE  BLOWPIPE,  ETC. — As  for  kaolinite  but  yielding  more  water  in  closed  tube. 

REMARKS. — Includes  indianaite,  a  compact  china  clay,  of  Lawrence  Co.,  Indiana, 
and  is  considered  to  be  the  principal  constituent  of  many  clay  beds  in  Alabama, 
Georgia;  Steinbruck,  Styria;  Elgin,  Scotland,  and  elsewhere. 

ALLOPHANE.— Al2SiO5  +  5H2O. 

A  translucent,  sometimes  wax-like  material  often  found  in  copper  and  iron  mines, 
filling  crevices  and  fissures  or  stalactitic  and  colored  by  intermixtures  of  chrysocolla, 
malachite  or  limonite;  also  in  cavities  in  marls  and  limestones.  H.,  3.  Sp.  gr., 
1.85  to  1.89. 

BEFORE  BLOWPIPE,  ETC. — Crumbles  but  is  infusible.  Becomes  blue  color  with 
cobalt  solution.  Gelatinizes  with  hydrochloric  acid. 

REMARKS. — Occurs  at  Richmond,  Mass.,  with  gibbsite.  In  marl  at  Saalfeld, 
Thuringia.  With  copper  minerals  in  Polk  Co.,  Tenn. 

MO NTMORILLONITE.— Probably  H2Al2Si4Oi2  +  n  aq. 

Very  soft,  often  soap-like,  white,  pinkish  or  variously  colored  material,  which 
softens  in  water  and  does  not  adhere  to  the  tongue  H.,  i  ?.  Sp.  gr.,  2  to  2.2. 

BEFORE  BLOWPIPE,  ETC. — Infusible,  loses  water. 

REMARKS. — Found  at  Branchville,  Conn,  (pink) ;  Montmorillon,  France  (rose  red) 
and  many  clay-like  materials  of  similar  properties  are  grouped  under  it  as  a  type,, 
such  as  stolpenite,  saponite,  erinite,  severite,  confolensite,  etc. 


CHAPTER  XXI. 

MINERALS  USED  AS  PRECIOUS  AND  ORNAMENTAL 

STONES. 

No  very  systematic  order  is  followed;  the  species  are  described 
in  two  groups: 

A.  The  Transparent  Stones. 

B.  The  Translucent  to  Opaque  Stones. 

Where  the  species  has  been  described  already  the  description  is 
not  duplicated  but  the  properties*  which  count  most  in  the  dur- 
ability and  beauty  of  the  stone  are  assembled  and  detailed,  and 
with  these  characters  something  is  given  as  to  occurrence.  Very 
little  is  stated  as  to  the  history,  methods  of  cutting,  famous  stones, 
superstitions,  etc.,  the  descriptions  in  fact  being  of  the  native 
uncut  mineral,  not  of  the  cut  stone. 

A.    THE  TRANSPARENT  STONES. 

DIAMOND. 

COMPOSITION. — C. 

GENERAL  DESCRIPTION. — Transparent,  isometric  crystals  with 
a  peculiar  adamantine  lustre  like  oiled  glass.  Usually  colorless  or 
slightly  tinted.  Also  translucent,  rough,  rounded  aggregates  and 
opaque  or  compact  masses  of  gray  to  black  color.  Especially 
characterized  by  a  hardness  exceeding  that  of  any  other  known 
substance. 

CRYSTALLIZATION.  —  Isometric.  Crystals  practically  always 
complete,  showing  no  signs  that  they  were  ever  attached  to  any 
support.  Usually  in  octahedrons,  Fig.  560,  with  smooth  faces  or 
with  triangular  markings,  often  with  edges  replaced  by  smaller 
faces,*  Fig.  559,  which  frequently  results  in  a  rounded  many-faced 

*  For  instance  the  DURABILITY  is  dependent  on  hardness,  density,  toughness  and 
absence  of  too  easy  cleavages;  the  beauty  upon  agreeable  color,  clearness  or  trans- 
parency, brilliancy  or  lustre  (itself  dependent  both  on  density  and  index  of  refraction) 
and  fire  (itself  dependent  on  dispersion). 

*  Hextetrahedral  modifying  faces  are  most  common,  while  rounded  hexoctahedra 
and,  more  rarely,  cubes  and  other  forms  occur.     Frequently  twinned  parallel  to  the 
octahedron. 

550 


MINERALS    USED   AS  PRECIOUS  STONES.  551 

crystal.  Very  perfect  cleavage  parallel  to  the  octahedron,  that 
is,  in  four  directions  at  angles  of  70°  31'  and  109°  29'  to  each  other. 
Readily  developed  by  a  sharp  blow  on  a  knife  held  in  proper  posi- 
tion, this  being  usually  preceded  by  a  scratch. 

FIG.  559.  FIG.  560.  FIG.  561. 


Physical  Characters. 

HARDNESS. — It  is  called  10,  but  the  stones  from  Borneo  and  N.  S. 
Wales  are  much  harder  than  those  from  other  localities  and  the 
Cape  stones  are  softer.  The  hardness  may  vary  in  parts  of  the 
same  stone. 

SPECIFIC  GRAVITY. — 3.145  to  3.518  (Crookes.)  Bort  and 
Carbonado  range  3.47  to  3.50. 

LUSTRE. — When  polished  peculiarly  brilliant,  typical  adaman- 
tine. When  unpolished  like  oiled  glass. 

COLOR. — Colorless  or  faintly  bluish  or  less  valued  "  off-colors" 
tinged  with  yellow,  brown  and  green.  More  rarely  decided  colors 
— red,  pink,  sapphire  blue  (a  little  greenish),  canary  yellow, 
decided  green. 

Optical  Characters. 

REFRACTION. — Single  with  index  very  high  and  constant.  2.4175. 
Often  local  double  refraction,  due  to  strain  (sometimes  from  in- 
cluded liquid  carbonic  acid). 

TOTAL  REFLECTION. — Critical  angle  very  small  24°  26',  this  per- 
mitting the  stone  to  be  cut  so  as  to  send  back  all  entering  light. 

COLOR  DISPERSION. — Very  high,  .044,  exceeded  only  by  titanite, 
.051,  and  demantoid,  .057.  Approached  by  zircon,  .038. 

ABSORPTION  SPECTRUM. — Not  constant,  sometimes  a  line  in  the 
violet. 

PERMEABILITY  TO  X-RAYS. — Highly  transparent. 

LUMINESCENCE. — Excited  in  some  diamonds  by  ultra-violet 
light  or  by  radium  or  X-rays  as  a  clear,  luminous  blue,  a  few 


552 


MINERALOGY. 


become  luminous  on  mere  rubbing  and  others  by  exposure  to 
sunlight. 

BEFORE  BLOWPIPE,  ETC. — In  fine  powder  is  slowly  burned  in 
presence  of  air  over  a  bunsen  burner  or  alcohol  lamp.     In  large 
mass  and  in  absence  of  air  is  very  little  affected  even  by  white 
heat.     Insoluble  in  acids. 
VARIETIES  : 

Ordinary. — In  rounded  crystals  with  distinct  cleavage. 

Bort. — Technically  any  diamond  or  fragment  of  diamond  not 
deemed  worthy  to  be  cut.  Crystallographically,  an  individual 
composed  of  many  smaller  crystals,  sometimes  enclosing  a  simple 
crystal,  oftener  not,  and  having  no  constant  directions  of  cleavage. 
Sometimes  the  little  crystals  are  radially  placed  and  their  edges 
form  a  rough  surfaced  sphere. 

Carbonado. — Black  massive  or  granular  material  from  Brazil. 

Formation  and  Occurrence. 

The  only  chance  of  studying  the  genesis  of  the  diamond  in 
place  is  in  South  Africa.  In  this  region  the  diamond-bearing 
ground  consists  of  comparatively  limited  areas  circular  or  oval  in 
form,  the  upper  portion  pale  yellow  and  crumbly,  but  lower  down 
firmer  and  bluish-green.  The  diamonds  are  distributed  through 
the  mass  sometimes  4  to  6  to  the  cubic  yard. 

The  minerals  with  the  diamonds  are  chiefly  broken  fragments  of 
serpentine,  diallage,  garnet,  magnetite,  etc.,  and  the  mass  extends 
downward  nearly  vertically  but  narrowing  somewhat  like  large 
" pipes"  or  cylinders  or  funnels  for  an  unknown  depth. 

The  older  theory  was  that  these  funnel-shaped  pipes  were 
volcanic  like  Vesuvius  and  that  the  diamonds  were  formed  with 
considerable  heat.  There  are  various  objections.  Volcanoes 
would  have  formed  elevations  and  there  would  have  been  over- 
flows. No  indications  of  this  exist  and  even  if  present  conditions 
resulted  from  erosion  there  would  have  been  as  a  result  of  the 
erosion  diamonds  and  rocks  from  the  pipes  in  the  ravines  and  water 
courses  in  the  vicinity,  but  there  never  are,  the  nearest  being  20 
miles  distant.  Moreover,  the  diamonds  have  retained  their  form 
and  brilliancy,  whereas  Herr  W.  Ludzi,  of  Leipzig,  fused  in  a 
crucible  at  about  2,000°  centigrade  the  "blue  ground"  containing 


MINERALS   USED  AS  PRECIOUS  STONES.  553 

diamonds  and  half  an  hour  of  this  resulted  in  a  marked  corrosion 
of  the  crystals. 

A  theory  which  seems  to  have  greater  probability  is  that 
the  blue  ground  was  forced  up  from  below  under  great  pressure 
by  steam  and  other  vapors.  The  diamonds  show  signs  of  this 
great  pressure,  often  containing  liquid  drops  of  carbonic  acid, 
and  the  blue  ground  being  heterogeneous  mixed-up  or  broken 
material,  apparently  originally  a  rock  of  such  material  as  pyroxene 
and  garnet,  some  of  which  is  often  included  boulder-like  in  the 
mass.  The  sides  of  the  contact  wall  also  show  smoothed  surfaces 
(slickensides)  and  scratches,  suggesting  the  up-and-down  motion 
several  times  of  this  material.  Such  a  theory  would  also  explain 
the  absence  of  the  rock  in  the  ravine  nearby,  because  the  pasty 
mass  of  mud  by  the  escape  of  the  vapors  would  settle  down  rather 
than  protrude  and  would  be  protected  from  erosion. 

The  Cutting  of  Diamonds. 

Until  the  fifteenth  century  diamonds  were  not  cut  but  worn 
in  the  natural  state  or  covered  with  a  green  varnish.  Some  little 
polishing  of  the  natural  faces  had  been  done  by  native  lapidaries 
and  to  disguise  the  presence  of  little  flaws  or  defects. 

In  1475  Louis  de  Berquem  discovered  that,  by  rubbing  one  stone 
with  another,  diamonds  could  be  cut  and  is  said  to  have  cut  three 
large  stones  for  Charles  the  Bold  of  Burgundy. 

Wheels  charged  with  diamond  dust  followed  but  as  late  as  1562 
the  only  forms  were  the  octahedron  and  the  table,  in  the  latter 
of  which  one  solid  angle  of  the  octahedron  had  been  cut  off  until 
the  resulting  new  face  was  one  half  the  width  of  the  stone. 

These  were  followed  by  the  rose  cut  with  a  flat  base  and  24 
triangular  facets,  and  the  brilliant,*  Fig.  561,  a  modification  of  the 
table  with  more  faces,  usually  58,  33  above  the  girdle,  25  below. 
Its  angles  are  chosen  so  that  the  incident  light  entering  falls  on 
the  lower  faces  at  angles  greater  than  the  critical  angle,  24°  26', 
and  is  totally  reflected,  preferably  through  the  inclined  faces,  thus 
producing  extreme  brilliancy  and  dispersion  of  the  light  or  color. 

Artificial  or  Synthetic  Diamonds. 

Diamonds  were  found  by  Friedel  in  the  Canon  Diablo  meteorite. 
Moissan  thereupon  experimented  by  saturating  iron  with  carbon, 

*  Said  to  have  been  discovered  by  Vincenzio  Peruzzi  in  1 790. 


554 


MINERALOGY. 


then  fusing  the  mass  and  pouring  quickly  into  a  vessel  containing 
water  and  mercury.  Minute  crystals  barely  visible  to  the  naked 
eye  were  obtained. 

Majorana  heated  carbon  in  the  electric  arc  and  while  hot 
blew  it  by  an  explosion  of  gunpowder  into  a  cavity  in  a  steel  block. 
Small  diamonds  resulted.  Pulverized  carbon  heated  on  iron,  wire 
in  the  electric  arc  in  an  atmosphere  of  hydrogen  yielded  diamond 
crystals. 

Silicates  like  the  blue  ground  fused  in  a  crucible  with  carbon 
yielded  small  diamonds. 

REMARKS. — Diamonds  have  been  known  in  India  for  over  3,000  years  but  do  not 
appear  to  have  reached  Europe  until  about  the  time  of  Caesar  Augustus.  They 
were  not  valued  for  their  beauty  but  for  supposed  supernatural  virtues  and  worn 
uncut  and  unpolished  and  indeed  until  the  fifteenth  century  had  at  most  their  natural 
faces  polished. 

India  supplied  practically  all  the  diamonds  until  1725,  when  the  Brazilian  deposits 
were  discovered  and  Brazil  in  turn  supplied  the  world  until  1867,  when  the  River 
diggings  of  South  Africa  and  a  little  later,  1870,  the  "dry  diggings"  or  Kimberley 
deposits  were  discovered.  These  still  are  the  great  source,  although  diamonds  are  or 
have  been  obtained  from  New  South  Wales,  Australia,  Rhodesia  and  German  South 
Africa.  A  few  diamonds  have  been  found  in  British  Guiana,  in  the  Shantung 
Province,  China,  and  in  the  gold  washings  in  the  Ural  Mountains,  and  in  four 
districts  in  the  United  States,  first  along  the  western  base  of  the  Sierra  Nevadas; 
second,  along  the  line  of  the  Terminal  Moraine  in  Wisconsin,  Michigan,  Indiana,  and 
Ohio,  presumably  coming  from  somewhere  in  Canada;  third,  in  Kentucky  and  Ten- 
nessee; fourth,  along  the  eastern  base  of  the  Appalachians  from  Virginia  to  Alabama. 

CORUNDUM.— Sapphire,  Ruby.     Described  on  p.  412. 

COMPOSITION. — AUOs.  Transparent  varieties  of  corundum  are 
known  as  rubies*  if  red",  sapphiresf  if  blue  and  fancy J  sapphires  if 
other  colors,  the  colorless  variety  is  called  white  sapphire.  The 
preferred  colors  are  pigeon  blood  or  purplish  red  and  velvety  corn 
flower  blue. 

Optical  Characters. 

UNIAXIAL  (— )  7-  1.766  to  1.744,  «-  1-757  to  1.765,  y-a  very 
constant  .0083  to  .009.  Color  dispersion  weak  .018.  Pleochroism 

*  Ruby  is  from  Latin  rubere  =  red. 

f  The  sapphire  of  the  ancients  was  lapis  lazuli,  but  in  course  of  time  this  became 
a  general  designation  of  blue  stone  and  later  of  the  blue  corundum.  Plato's  adamant 
was  supposed  to  have  been  sapphire.  Hyacinth  was  also  used  for  stone  apparently 
sapphire. 

%  Fancy  sapphires  are  sometimes  known  as  "  oriental  "  topaz,  amethyst,  etc. 


MINERALS   USED   AS  PRECIOUS  STONES. 


555 


usually  distinct,  sometimes  strong.  Twin  colors  varying  with 
color  and  locality. 

LUMINESCENCE. — Very  varied.  Burmese  rubies  brilliant  red 
with  ultra-violet  light,  Siam  rubies  no  luminescence.  Synthetic 
rubies  more  brilliant  even  than  Burmese.  Ceylon  rubies  phos- 
phorescent (yellow)  on  heating. 

EFFECTS  OF  HEAT. — Ruby  loses  color  but  cools  through  white 
and  green  to  the  original  tint.  Sapphire  strongly  heated  is  decolor- 
ized in  part  and  if  pale  violet  or  yellow  may  become  white,  if  deep 
violet  may  become  rose  colored. 

FIG.  562. 


Corundum  Crystals,  Ceylon.     U.  S.  National  Museum. 


BEAD  TESTS. — Synthetic  and  natural  rubies  color  salt  of  phos- 
phorus beads  green  in  R.  F. 

OCCURRENCE. — Very  largely  from  gravels  or  alluvial  deposits 
sometimes  in  place  as  in  Yogo  Gulch,  Montana,  and  Siam. 

SAPPHIRES. — Ceylon. — Chiefly  from  the  gravels  in  Sahara  Gamuwa  province 
with  spinel,  zircon,  beryl,  topaz,  etc.  These  gravels  extend  far  below  water  level, 
and  in  one  case  120  ft.  and  underlie  swamps  and  rice  fields.  The  crystals  are 
pyramidal  (while  the  corundum  in  place  is  prismatic). 

Siam. — Probably  half  the  sapphires,  including  the  finest  corn  flower  blue  stones 
are  from  Siam. 

India. — In  Kashmir  in  the  Himalayas,  14,000  ft.  above  sea  level,  fair  quality 
stones  occur  in  a  hard  rock  (gneiss)  and  were  found  in  considerable  quantities  at  the 
foot  of  a  precipice  where  a  landslide  had  occurred. 


556 


MINERALOGY. 


FIG.  563. 


Australia. — Many  colors,  but  none  red  or  fine  blue,  are  found  near  Anakie, 
Queensland,  in  a  gravel  of  decomposed  basalt. 

Montana. — At  Yogo  Gulch  in  place  in  a  dike  which  cuts  through  limestone  and 
in  gravels  on  the  Upper  Missouri  River.  The  colors  are  given  as  deep  and  light 
aquamarine,  greens,  yellows,  pinks,  amethystine.  The  lustre  is  peculiar,  almost 
metallic. 

RUBIES. — Burmah. — The  most  valued  rubies  come  from  Mogok  north  of 
Mandaly  in  Upper  Burmah,  4,000  ft.  above  sea. 

They  occur  in  a  sort  of  clay  called  "  byon,"  considered  to  be  the  result  of  the  decay 
of  a  crystalline  limestone  containing  also  spinels,  sapphires,  and  tourmalines.  Also 
found  in  a  gravel  bed  underlying  alluvial  deposits  in  Mogok  Valley. 

Siam. — Darker  colored  rubies  are  found  in  Siam  associated  with  red  spinel  and 
sapphires  at  the  Navony  Mine  near  Bangkok.  Some  also  are  found  with  the 
sapphires  at  the  Pailinh  Sapphire  Mine  in  eastern  Siam. 

Ceylon. — Not  found  in  place  and  only  comparatively  rarely  in  the  gravels.  They 
are  never  the  true  Burmese  red,  though  often  more  brilliant. 

Synthetic  Rubies  and  Sapphires. 

Corundum  is  synthetically  made  by  the  method  of  Verneuil  in 

pear-shaped  drops  or  "boules," 
Fig.  564,  which  are  true  anhedral 
crystals,  and  are  character  for 
character,  except  shape,  identical 
with  the  natural  ruby  or  sapph- 
ire.* They  bear  the  same  rela- 
tion to  the  natural  stone  that 
the  ice  of  the  pond  does  to  the 
manufactured  ice  and  while  easily 
distinguished  before  cutting,  are 
distinguished  afterwards  only 
with  difficulty  by  inclusions,  mode 
of  distribution  of  color,  etc. 
The  apparatus  of  Veneuil,  Fig. 
563,  is  an  inverted  oxyhydrogen 

•^^JKurion  ~  blowpipe,  in  which  the  raw  ma- 

ll terial,  a  carefully  prepared  pow- 

der, is  sifted  regularly  through  a 
sieve  into  an  enlargement  of  the 
oxygen  tube,  the  speed  being 
regulated  by  a  tapping  hammer, 
and  is  carried  with  the  oxygen 

*  A.  J.  Moses,  Amer.  Jour.  Sci.,  XXX,  271,  1910. 


FIG.  564. 


MINERALS   USED  AS  PRECIOUS  STONES.  557 

to  the  fusion  chamber  and  falls  as  a  melted  drop  on  the  sup- 
port, where  it  gradually  builds  up  the  boule. 

STONES   RESEMBLING   THE   SAPPHIRE. 

IOLITE. — Water  sapphire.  Described  on  p.  529.  The  stones  that  are  usually 
cut  are  light  to  dark  smoky  blue.  It  also  occurs  violet. 

Pleochroism  very  strong.  The  principal  colors — smoky  blue  and  yellowish  white 
— being  visible  to  the  unaided  eye.  It  is  therefore  cut  with  the  table  face  perpen- 
dicular to  the  direction  of  deepest  blue. 

Occurrence  Cutting  Material. — Chiefly  found  in  water-worn  masses  in  the  river 
gravels  of  Ceylon.  One  piece  in  the  British  Museum  weighs  177  grams.  The  Had- 
dam,  Conn.,  material  is  sometimes  cut.  Other  localities  are  Bodenmais,  Bavaria, 
Finland,  Sweden. 

BENITOITE.— BaTi(SiOs)3.  This  stone  was  discovered  in  1906  and  at  first 
cut  and  sold  as  sapphire.  Few  stones  exceed  2  carats,  one  was  7  carats.  The 
characters  of  importance  are  as  follows:  H.,  6.5.  Sp.  gr.,  3.64  to  3.72. 

Color. — Varies  from  deep  blue  with  a  violet  tint  to  pure  blue  or  a  lighter  shade, 
sometimes  perfectly  colorless. 

Refraction  and  Indices  of  Refraction. — Doubly  refracting,  uniaxial,  positive. 
Ordinary  index  is  1.757  and  the  extraordinary  1.804. 

Birefringence  strong,  .047  (Eppler  says  .03). 

Dispersion  strong,  producing  considerable  fire. 

Pleochroism  strong,  ordinary  ray  white — extraordinary  greenish  blue  to  reddish 
blue.  As  light  transmitted  perpendicularly  to  the  base  is  practically  colorless,  the 
gem  should  be  cut  with  a  table  parallel  to  the  principal  axis  which  is  contrary  to  the 
rule  for  sapphire. 

Effects  of  Heat. — Color  unchanged  until  it  fuses  quietly  to  a  transparent  glass  at 
about  3.  Salt  of  phosphorus  bead  violet  in  reducing  flame. 

Effects  of  Acid. — Practically  insoluble  in  hydrochloric  acid,  readily  attacked  by 
hydrofluoric  acid  and  dissolves  in  fused  sodium  carbonate. 

Occurrence. — Occurs  in  veins  and  crusts  of  natrolite  in  a  hornblende  schist  of  the 
Coast  Range  of  California.  It  occurs  with  the  rare  mineral  neptunite,  in  Diablo 
Range,  near  the  headwaters  of  San  Benito  River,  California. 

CYANITE. — Composition. — Al2SiO5.     Described  on  p.  519. 
Azure  to  cornflower  blue  varieties  only  are  cut.     Green  and  white  occur. 
There  are  many  distinctions  from  sapphire  such  as  hardness,  5  to  7,  numerous 
striations  and  cracks,  lower  indices,  7  1.7280:  1.712,  lower  specific   gravity,  3.56  to 

3-67. 

Occurrence  of  Cutting  Material. — The  finest  sky  blue  crystals  come  from  Mt. 
Campione,  St.  Gothard,  Switzerland;  Zillerthal  and  Pfitschthal,  Tyrol;  India 
(where  it  is  sorted  with  sapphire  and  sold  at  good  prices),  near  the  peak  of  Yellow  Mt., 
Bakersville,  N.  C.,  and  Diamantina,  Brazil. 

HAUYNITE.     Composition. — CaSO4  2(Na2Ca)Al2(SiO4)2.     Described  on  p.  500. 

Occurs  occasionally  as  transparent  sky-blue  grains,  and  is  cut.  Its  isotropic 
character  and  very  low  index,  1.49,  distinguish  it. 

Occurrences  Cutting  Material. — Near  Albano,  Italy,  in  Auvergne,  France,  and  at 
Niedermendig  on  the  Rhine. 


558 


MINERALOGY. 


SPINEL.*— Balas  Ruby. 

COMPOSITION.— Mg(AlO2)2,  (MgO  28.2,  A12O3  71.8  per  cent.) 
Iron,  manganese  and  chromium  are  sometimes  present. 


FIG.  569. 


FIG.  570. 


FIG.  571. 


GENERAL  DESCRIPTION. — Usually  in  octahedral,  simple  or 
twinned  crystals,  varying  in  color  according  to  composition,  and 
even  in  the  gravels  which  round  the  still  harder  ruby  retaining 
much  of  their  sharpness. 

Spinel  is  not  well  known  as  a  gem  partly  because  the  red  varieties  were  until 
comparatively  recently  not  distinguished  by  jewelers  from  the  ruby.  Some  great 
historic  rubies  have  proved  to  be  spinels. 

CRYSTALLIZATION. — Isometric,  the  octahedron  p  or  this  modi- 
fied by  the  dodecahedron  d  or  the  trapezohedron  o  =  (a  :  $a  :  30) ; 


VARIETIES  : 

The  transparent  varieties  most  valued  are : 

Balas  Ruby.     Rose  red  or  pink.     Ruby  Spinel.     Clear  red. 

These  varieties  are  said  always  to  show  a  pale  yellow  reflection  from  the  interior 
of  the  stone. 

Less  valued  are:  Rubicelle,  yellow  to  orange;  Sapphirine,  steely 

blue;  Almandine,  purple  to  violet. 

The  opaque  varieties  include:  Ceylonite  (Iron  Magnesia  Spinel). 

—Dark-green,  brown,  black,  usually  opaque.     Picotite  (Chrome 

Spinel). — Yellowish  to  greenish-brown,  translucent. 

Physical  Characters.     H.,  8  to  8.5.     Sp.  gr.,  3.5  to  3.7.     (Cey- 
lonite 4.1.) 

LUSTRE,  vitreous.  COLOR,  as  given  and  intermediate. 

STREAK,  white.  CLEAVAGE,  octahedral  difficult. 

*  From  a  word  for  a  "little  spark,"  referring  to  the  fiery  red  of  most  prized  kind. 


MINERALS    USED   AS  PRECIOUS  STONES.  559 

Optical  Characters. 

Singly  refracting.  Indices  of  red  and  blue  stones  1.716  to  1.720. 
Deep  violet  ones  1.730.  Color  dispersion  weak,  .020.  Very 
slightly  penetrated  by  X-rays. 

REMARKS. — The  common  opaque  spinels  occur  occasionally  in  igneous  rocks, 
picotite  with  chromite,  ceylonite  with  magnetite,  but  are  more  common  in  metamor- 
phosed limestone,  both  contact  and  enclosed  in  schists. 

The  gem  varieties  are  also  most  frequent  in  limestones  and  dolomites.  Corundum 
is  a  common  associate.  The  principal  localities  for  gem  spinel  are  the  ruby-bearing 
limestones  of  Burma  and  Siam,  which  yield  red  varieties,  and  the  gem  gravels  of 
Ceylon,  which  yield  blue  and  violet  varieties.  Other  localities  are  Expailly,  France; 
Badakschan,  Tartary;  and  in  this  country  gem  specimens  have  been  obtained  at 
Hamburg,  N.  J.;  San  Luis  Obispo,  Cal.,  and  Orange  County,  N.  Y.  The  crystals 
also  occur  in  many  localities  in  North  Carolina,  Massachusetts  and  near  the  New 
York  and  New  Jersey  line. 

BERYL. — Emerald,  Aquamarine.     Described  on  p.  552. 

COMPOSITION. — Be3Al2(SiO3)6. 

This  mineral  furnishes  the  gems,  emerald,  aquamarine,  golden 
beryl,  morganite  and  heliodore. 

Optical  characters  needing  further  detail  are : 

REFRACTION  AND  INDICES  OF  REFRACTION. — Doubly  refracting, 
uniaxial  and  optically  negative. 


y 

a 

y—  a 

Range 

i  572  to  1.598 

1.567  to  1.59 

.005  to  .008 

Colombian  emerald  

1.584 

1.578 

.006 

Siberian  aquamarine 

1.582 

1.576 

.OO6 

Morganite  

1.598  ? 

1-59 

.008 

BIREFRINGENCE  weak  .005.     DISPERSION  small. 
PLEOCHROISM  is  usually  faint  but  the  South  American  emerald 
gives  yellowish-green  and  bluish-green. 

EMERALD. — Grass  green,  inclining  rather  to  blue  than  yellow.  It  has  no  fire, 
is  only  moderately  hard,  usually  flawed  ("an  emerald  without  a  flaw"),  and  not  as 
brilliant  as  some  other  green  stones  like  hiddenite  and  demantoid,  yet  from  ancient 
times  its  color  has  given  it  high  rank. 

The  emerald  of  ancient  times  came  from  Upper  Egypt.  The  locality  was  lost 
and  refound  in  1820  in  the  mountain  range  to  the  west  of  the  Red  Sea,  where  both 
emerald  and  beryl  occur  in  micaceous  and  talc  schists.  The  emeralds  are  inferior 
to  those  from  Colombia. 

The  three  great  districts,  discovered  in  Colombia  in  1558  by  the  Spaniards  soon 
after  their  conquest  of  Peru,  were  worked  irregularly.  That  of  Muzo,  75  miles  north- 


560 


MINERALOGY. 


west  of  Bogota,  is  still  working  and  is  the  chief  source  of  the  emeralds  of  the  best 
grade.  They  are  said  to  be  sent  chiefly  to  India  to  be  cut.  The  localities  of  the 
other  two  were  lost  and  one  only  was  rediscovered  in  1896,  the  other  is  still  "lost." 

Fine  emeralds,  but  inferior  to  the  Muzo  stones,  come  from  the  Ural  Mts.  near 
Ekakrinenberg  and  the  Salzburg  Alps  in  Austria  have  yielded  emeralds  from  the 
time  of  the  Romans  down. 

Other  localities  are:  Arendal,  Norway;  Topsham,  Maine;  Alexander  Co.,  N.  C. 

AQUAMARINE. — "Green  like  the  sea,"  that  is  deep,  blue-green  and  grading 
from  this  towards  colorless. 

It  is  much  used  for  brooches,  and  pendants,  occurs  in  large  quantities  and  fine 
grade  both  at  Minas  Novas  and  other  parts  of  Brazil  and  at  Mursinka,  Urals,  and 
of  fine  grade  at  Adun  Tschilon,  Siberia.  Poorer  grades  are  abundant. 

GOLDEN  BERYL  of  light  and  deep  golden  yellow  is  found  in  Macon  Co.,  N.  C., 
Delaware  Co.,  Penn.,  etc. 

MORGANITE,  from  Maharita,  Madagascar,  is  of  pure  rose  pink  color. 

HELIODORE,  from  German  S.  W.  Africa,  golden  yellow  by  daylight,  green  by 
artificial  light  is  said  to  be  beryl. 

CHRYSOBERYL.— Alexandrite,  Cymophane. 

COMPOSITION. — BeAl2O4,  (BeO  19.8,  A12O3  80.2  per  cent.),  with 
oxides  of  chromium  and  iron  giving  the  color. 

GENERAL  DESCRIPTION. — Pale  green  or  yellowish  tabular  crys- 
tals; thicker  deep  emerald-green  crystals,  which  by  transmitted 
light  are  a  purplish  red ;  and  rolled  pebbles  sometimes  with  an 
internal  opalescence. 

CRYSTALLIZATION. — Orthorhombic  a  :  b  :  c  =  0.470  :  i  :  0.580. 
Often  flat  contact  twins  with  feather-like  striations,  Fig.  573, 


FIG.  572. 


FIG.  573- 


Urals. 


Haddam,  Conn. 


Alexandrite  occurs  in  simple,  Fig.  572,  or  twinned  crystals  snowing 
unit  pyramid  p  and  prism  m  with  brachy-pyramid  r  =  (2a  :  b  :  2c), 
ji2ij;  and  prism  n  =  (2 a  :  b  :  oo  c),  {120}.  Supplement  angles 

rr  =  72°  17'. 


are  mm  =  50°  21';  nn  =  86°  28';  pp  =  40° 


MINERALS   USED  AS  PRECIOUS  STONES.  561 

VARIETIES. — Alexandrite,  the  deep  green  variety,  which  is  so 
called  because  it  was  found  in  the  emerald  mines  of  the  Urals  on 
the  birthday  of  the  Emperor  Alexander  II.  By  daylight  it  is 
bluish  to  olive  green  in  color  and  by  lamp-  or  gas-light  raspberry 
red,  the  cause  of  the  change  being  the  strong  absorption  of 
yellow  and  blue  rays,  the  residual  product  varying  with  the  source 
of  light.  For  instance,  with  the  tungsten  light  it  is  neither  red 
nor  green  but  intermediate. 

Fine  stones  are  scarce,  the  best  coming  from  near  Ekaterinberg,  poorer  from 
Tokowaja. 

Larger  stones  of  good  quality  come  from  Ceylon  and  others  from  the  Weld 
River,  Tasmania. 

Cymophane  or  Cats  Eye. — Yellowish-green  and  with  minute 
parallel  cavities.  If  cut  cabochon  with  the  rounded  surface 
parallel  to  these  a  sharp  line  of  opalescent  light  appears  crossing 
the  stone  at  right  angles  to  the  cavities,  which  seems  to  float  in 
the  surface  as  the  stone  is  moved. 

Principal  locality  is  Ceylon,  others  come  from  Brazil. 

Chrysoberyl  or  Oriental  Chrysolite. 

Chrysoberyl  or  Oriental  Chrysolite. — Color,  pale  yellowish  green. 

From  Minas  Novas,  Brazil,  and  some  from  Rhodesia  and  Haddam,  Conn.  It  is 
often  confused  with  the  yellow  spodumene  from  Brazil. 

Physical    Characters.     H.,     8.5.     Sp.     gr.,    Alexandrite    3.644. 
Others  3.68  to  3.78. 

LUSTRE,  vitreous   to   greasy  but   less  greasy   than   chrysolite. 
COLORS. — As  described  under  varieties. 

Optical  Characters. 

Biaxial  (+).  Axial  plane  (oio).  Acute  bisectrix  c .  7  =  1.750 
to  1.757,  <*  =  I-742  to  i.749»  7  -  a  =  .009. 

PLEOCHROISM. — Very  strong  in  alexandrite  in  columbine  red, 
orange  and  emerald  green.  The  cymophane  and  oriental  chryso- 
lite show  less  strong  pleochroism. 

ACTION  X-RAYS. — Rather  easily  penetrated. 

BEFORE  BLOWPIPE,  ETC. — Infusible.  In  powder,  is  turned  blue 
by  cobalt  solution.  Insoluble  in  acids. 

REMARKS. — Occurrences  as  described  under  varieties.  No  fine  gems  have  been 
found  in  the  United  States,  although  the  mineral  occurs  sparingly  in  Stowe,  Peru  and 
Canton,  Me.,  New  York  City,  and  Greenfield,  N.  Y.,  Haddam,  Conn. 

37 


562  MINERAL  OGY. 

OTHER   BERYLLIUM    GEMS. 

Beryllium  which  has  no  other  economic  value  is  the  chief 
element  not  only  in  beryl  and  chrysoberyl  but  in  the  following 
species  cut  as  precious  stones. 

EUCLASE. — Be(AlOH)SiO4.  Sea  green  or  pale  blue  or  colorless  crystals  with 
vitreous  lustre.  It  takes  a  brilliant  polish  and  when  cut  greatly  resembles  the  aqua- 
marine. It  is  very  seldom  cut,  both  because  the  crystals  are  valued  by  collectors 
and  because  of  the  very  easy  cleavage  to  which  it  owes  its  name. 

Found  in  Brazil  at  Villa  Rica.  Minas  Geraes  in  the  topaz  locality,  but  never 
in  the  same  druse.  Also  in  diamond  sand  at  Bahia.  In  Urals  on  Sanarka  River  in 
the  gold  washing  and  associated  with  topaz.  Other  localities  are  Peru  and  Tasmania. 

PHENACITE. 

COMPOSITION. — Be2SiO4  (BeO  45.55,  SiO2  54.45  per  cent.). 

GENERAL  DESCRIPTION.  —  Colorless,  transparent,  rhombohedral  crystals,  usually 
small,  frequently  lens-shaped.  Sometimes  yellowish  and  sometimes  in  prismatic  forms. 
Harder  than  quartz. 

FIG.  574.  FIG.  575. 


Mt.  Antero,  Col.  Florissant,  Col. 

CRYSTALLIZATION.  —  Hexagonal.  Class  of  third  order  rhombohedron,  p.  54.  Axis 
c==  0.661.  Supplement  angles  xx  —  75°  $7'  ;  rr  =  63°  24'.  Optically  -f-  . 

PHYSICAL  CHARACTERS.  —  Transparent  to  nearly  opaque.  Lustre,  vitreous.  Color, 
colorless,  yellow,  brown.  Streak,  white.  H.  7.5  to  8.  Sp.  gr.  2.97  to  3.  Brittle. 
Cleavage,  prismatic. 

BEFORE  BLOWPIPE,  ETC.  —  Infusible  and  unaffected  by  acids.  Made  dull  blue  by 
cobalt  solution. 

The  colorless  water  clear  varieties  when  cut  possess  considerable  brilliancy,  about 
that  of  a  white  sapphire. 

OCCURRENCE. — In  granite  pegmatites,  quartz  porphyry  and  mica  schist.  Cut- 
able  stones  are  found  in  the  Urals  at  the  emerald  mines  at  Stretinsk  and  at  Miask. 
In  Colorado  at  Pikes  Peak  and  Topaz  Butte  and  Mount  Antero.  In  Brazil  at  Minas 
Geraes. 

BERYLLONITE.— NaBePO4.  A  clear  colorless  mineral  occasionally  cut.  The 
transparency  and  brilliancy  of  the  stone  resembles  that  of  topaz,  but  lack  of  "fire" 
and  softness  are  against  it.  H.,  5.5. 

OCCURRENCE. — Found  loose  among  the  disintegrated  material  of  a  granite  vein 
at  Stoneham,  Maine. 

GADOLINITE. — Be2FeY2Si2Oio,  is  occasionally  cut  as  an  opaque  black  stone. 


MINERALS    USED   AS  PRECIOUS  STONES.  563 

ZIRCON. — Hyacinth.     Matura  Diamonds.     Described  on  p.  314. 
COMPOSITION. — ZrSiCX 

Transparent  zircons  possess  the  qualities  which  should  make  them  rank  high, 
namely,  brilliancy,  strong  color  dispersion,  durability  and  agreeable  colors  including 
the  fine  golden  yellow,  aurora  red  to  deep  red  and  leaf  green. 

COLORS  AND  COLOR  NAMES. — Zircon,  brown,  violet,  green  (leaf- 
green),  blue. 

Hyacinth*  aurora  red,  sometimes  deep  red. 

Jacinth,  yellow — often  golden. 

Jargon,  grayish- white  or  white,  especially  if  not  hard. 

Matura  Diamonds,  colorless  (usually  made  so  by  heating). 

Notable  Characters. 

The  characters  following  would  seem  to  indicate  at  least  two 
structurally  different  substances,  one  isotropic  or  nearly  so,  the 
other  tetragonal. 

CRYSTALLIZATION. — Sharp,  tetragonal  crystals.  The  Ceylon 
pebbles,  however,  show  no  crystal  faces. 

REFRACTION  AND  INDICES  OF  REFRACTION. — Doubly  refracting, 
uniaxial  and  positive,  but  with  wide  differences,  some  with  both 
indices  close  together  and  ranging  from  1.79  to  1.84.  Others  with 
ordinary  ranging  from  1 .92  to  1 .93  and  extraordinary  1 .96  to  1 .99. 

BIREFRINGENCE. — In  some  almost  zero,  in  others  very  strong, 
as  much  as  .06. 

Other  characters  are : 

LUSTRE. — Adamantine — approaching  that  of  the  diamond.  It 
is  increased  by  heating. 

COLOR  DISPERSION.— Very  high,  .038,  diamond  being  only  .044. 
Hence  considerable  fire,  though  inferior  to  that  of  the  diamond. 

ABSORPTION  SPECTRUM. — Often  show  lines  characteristic  of 
uranium,  corresponding  to  wave-lengths  651,  588  and  512.  Many 
zircons  do  not  show  the  bands. 

PLEOCHROISM. — Exceedingly  faint  even  in  most  highly  colored 
stones. 

ACTION  X-RAYS. — Practically  opaque. 

*  Hyacinth,  from  an  old  Indian  word  originally  used  for  sapphire,  then  especially 
for  yellow  sapphire  and  generally  for  other  yellow  stones,  then  more  definitely  for 
yellow  zircon  and  garnet.  Now  queerly  twisted  to  the  more  red  stones  while  the 
yellow  are  called  by  another  spelling  of  the  same  word,  Jacinth. 


MINERALOGY. 

LUMINESCENCE. — Sometimes  luminescent  during  grinding  or  if 
heated  on  Bunsen  burner. 

SPECIAL  TEST. — Under  the  microscope  many  zircons  show  a 
"feathery"  appearance  called  "ratine"  and  described  as  resem- 
bling a  liqueur  poured  in  water. 

BEFORE  BLOWPIPE,  ETC. — Infusible  but  at  about  500°  C.,  the 
color  is  weakened  and  may  be  destroyed.  The  green  may  become 
fine  yellow  and  the  pale  brown  become  colorless.  Some  colorless 
stones  from  Tasmania  become  brown  on  heating.  Insoluble  in 
acids. 

OCCURRENCE. — The  finest  stones  come  from  Ceylon.  Fine  red  stones  are  brought 
from  central  Queensland  and  from  New  South  Wales.  Small  hyacinths  and  deep 
red  stones  are  found  at  Expailly,  France.  Rounded  pebbles  in  Tasmania.  Other 
localities  in  Germany  and  Bohemia. 

TOPAZ. — Precious  Topaz.     Described  on  p.  523. 

COMPOSITION. — Al^SieC^Fio.  The  best  known  topaz  is  yellow 
or  sherry  to  brownish  yellow.  Decided  blues  are  called  Brazil 
sapphires.  Red  or  pink  topaz  (usually  the  result  of  heating  the 
Brazil  yellow  stone)  are  known  as  Brazil  rubies. 

Much  of  the  so-called  topaz  is  yellow  quartz  (citrine  or  burnt  amethyst).  This 
though  unsatisfactory  can  claim  old  usage,  for  it  is  generally  admitted  that  topaz 
first  meant  a  yellow  chrysolite  from  Topazion,  an  island  in  the  Red  Sea,  and  later 
the  name  stood  for  any  yellow  gem  and  in  this  sense  it  is  still  used  by  the  jewelers. 

Brazil  and  the  Urals  are  the  chief  sources  of  gem  topaz. 

Brazil  in  decomposed  rock  and  gem  gravels  at  Ouro  Preto,  Villa  Rica  and 
Minas  Novas,  as  wine  yellow,  blue,  pinkish  and  brownish  yellow,  light  green  and 
colorless. 

Urals. — Fine  green  and  blue  from  Alabastika,  Perm  and  Miask.  Reddish  from 
gold  washings  at  Troisk,  pale  brown  from  near  Nertschinsk. 

Other  localities  are:  Cairngorm,  Scotland.  Sky  blue  pebbles.  Tasmania.  Color- 
less, sea-green  and  blue.  Japan.  Colorless  and  bluish.  San  Luis  Potosi,  Mexico 
and  Pike's  Peak,  Colorado.  Colorless. 

DANBURITE. — A  borosilicate  of  lime,  occurring  in  considerable  quantity  as 
pale  wine  colored  orthorhombic  crystals  at  Russell,  N.  Y.  Has  been  found  in  Japan 
as  colorless  transparent  crystals  greatly  resembling  topaz  which  when  cut  show 
considerable  brilliancy.  H.,  7.5.  Sp.  gr.,  2.97  to  3.02. 

TOURMALINE.— Rubellite,  Etc.     Described  on  p.  524. 

COMPOSITION.— R18B2(SiO5)4.  R  chiefly  Al,  K,  Mn,  Ca,  Mg,  Li. 
This  mineral  yields  numerous  transparent  stones  of  many  colors. 


MINERALS   USED  AS  PRECIOUS  STONES.  565 

The  green  and  red  and  brown  are  most  cut.  The  variety  names* 
are  purely  color  names  and  are  not  much  used;  more  often  the 
name  tourmaline  with  the  prefix  green,  red,  etc. 

Oddities  are  cats  eye  tourmaline  and  green  tourmaline,  ruby 
red  in  artificial  light  (Ekaterinenberg). 

The  most  notable  characters  are  the  strong  pleochroism  and 
absorption,  the  development  by  friction  or  heat  of  -f  and  — 
charges  of  electricity  at  opposite  ends  of  the  c  axis,  and  the  fusi- 
bility sometimes  easy,  sometimes  difficult. 

OCCURRENCE. — The  great  localities  are  Minas  Novas  and  Arrasuhy.  Brazil 
(green  and  red),  Ekaterinenberg  and  Transbaikal,  Russia  (pink,  blue,  green  and  red); 
Pala  and  Mesa  Grande,  California  (pink,  green  and  blue),  Ceylon  (the  yellow 
"turumali"  from  which  the  name  tourmaline  came).  Other  localities  are  Burmah, 
Madagascar,  Mt.  Mica  and  Auburn,  Maine. 

SPODUMENE.— Hiddenite,  Kunzite.     Described  on  p.  429. 

COMPOSITION. — LiAl(SiO3)2,  with  traces  of  chromium,  or  manga- 
nese in  the  colored  varieties. 

This  species  yields  stones  with  beautiful  lustre. 

VARIETIES  AND  THEIR  OCCURRENCE. 

HIDDENITE. — Yellowish  to  deep  emerald  green  tinged  with  yellow.  Color 
attributed  to  chromium.  Ends  of  crystals  usually  different  color. 

From  Stony  Point,  N.  C.,  at  the  Emerald  Mine.  About  200  carats  were  found. 
The  largest  crystal  would  have  yielded  a  stone  of  s|  carat. 

KUNZITE. — Lilac,  pink,  colorless.  The  crystals  often  pale,  observed  through 
the  prism  and  rich  amethystine  observed  transversely.  Color  attributed  to  manga- 
nese. 

Found  near  the  deposit  of  colored  tourmalines  at  Pala,  California.  One  crystal, 
the  Pala  Princess,  weighs  2,444^  carats. 

SPODUMENE. — Yellow  to  colorless  with  a  touch  of  green. 

Found  in  Brazil,  Minas  Geraes,  with  chrysoberyl  (often  confused  with  it). 

Notable  Characters. 

Hiddenite  is  strongly  pleochroic.  Kunzite  is  pleochroic,  in  violet  and  yellow,  or 
with  paler  crystals,  pink  and  nearly  white. 

Kunzite  becomes  luminescent  with  X-rays  or  radium  or  ultra-violet  light 

*  Achroite — colorless.  Indicolite — indigo  blue  or  dark  blue.  Brazilian  Sapphire 
— lighter  blue  but  never  sapphire  tinted.  Rubellite — rose  red  and  pink.  Siberite — 
violet  red.  Siberian  ruby — dark  red.  Brazilian  emerald — dark  green  but  never 
emerald.  Ceylon  peridot — yellow.  Brazilian  peridot — yellowish  green.  Ceylon 
chrysolite — greenish  yellow.  Schorl — black. 


566  MINERAL  OGY. 

CHRYSOLITE. — Olivine,  Peridot.     Described  on  p.  513. 
COMPOSITION. — (Mg.Fe)2SI04. 

Chrysolite,  the  golden  stone  of  Pliny,  was  yellow  topaz  and  topazius  was 
chrysolite.  This  has  gradually  been  inverted.  Peridot  is  of  uncertain  origin  and 
is  apparently  the  same  as  Pliny's  callaina. 

PERIDOT,  sometimes  called  the  evening  emerald,  is  deep  bottle 
green  'Mike  tourmaline  with  a  dash  of  yellow"  to  less  attractive 
olive  green.  The  approved  color,  "like  that  seen  in  looking 
through  a  delicate  green  leaf." 

CHRYSOLITE  is  pale  greenish  yellow. 

Notable  Characters. 

The  stones  are  too  soft  for  ring  stones  (H.,  6.5)  but  have  a  very 
brilliant  somewhat  oily  lustre  when  polished. 

The  Birefringence  is  .036,  higher  than  most  gem  stones  and 
usually  easily  recognized  in  a  cut  stone  by  the  doubling  of 
edges  as  seen  through  the  table  face. 

The  Pleochroism  is  faint,  one  image  more  yellow  than  the  other, 
stronger  in  olive-colored  stones  Peridot  may  give  straw  yellow 
and  green. 

ACTION  OF  HEAT. — Dark  stones  are  made  lighter  in  the  oxidiz- 
ing flame,  becoming  more  yellowish  brown  and  in  the  reducing 
flame  more  green. 

OCCURRENCE  OF  CUTTING  MATERIAL. — Most  of  it  comes  from  the  Island  of  St. 
John  in  the  Red  Sea.  Crystals  yielding  stones  Up  to  80  carats  in  weight  are  found. 
It  is  believed  that  this  is  the  long  lost  source  of  the  fine,  large  stones  so  common  in 
European  altar  decorations. 

Arizona  and  New  Mexico  furnish  dark  yellowish  green  peridot  without  crystal 
form.  Queensland  and  Upper  Burma  supply  light  green  stones. 

STONES   RESEMBLING   CHRYSOLITE. 

TITANITE  OR  SPHENE.— CaTiSiOs.  This  mineral,  described  p  525,  fur- 
nishes stones  of  great  brilliancy  and  fire  of  about  the  colors  of  chrysolite  and  brown 
topaz.  They  are,  however,  too  soft  for  much  wear  H.  =  5.5. 

COLORS. — Yellowish  green,  suggesting  chrysolite  or  demantoid  and  brownish 
yellow  resembling  topaz. 

LUSTRE.— Very  brilliant,  almost  adamantine. 

PLEOCHROISM. — Vivid  with  twin  tints,  green,  yellow  and  reddish. 

REFRACTION  AND  INDICES  OF  REFRACTION. — Double  refracting,  biaxial  positive. 
The  smallest  index  varies  from  1.888  to  1.917,  the  largest  from  i  914  to  2.053. 

BIREFRINGENCE.— .12.  So  large  that  the  doubling  of  the  opposite  edges  when 
viewed  through  one  of  the  faces  is  obvious  to  the  unaided  eye,  even  in  a  thin  stone. 


MINERALS    USED   AS  PRECIOUS  STONES.  567 

COLOR  DISPERSION. — .051.  Greater  even  than  that  of  the  diamond  and  result- 
ing in  a  great  deal  of  "  fire." 

OCCURRENCE  OF  CUTTING  MATERIAL. — Switzerland,  in  St.  Gothard;  Tyrol, 
Pfitschthal;  New  York  at  Tilly  Foster  in  yellow  to  brown;  Pennsylvania,  Bridge- 
water. 

DIOPSIDE. — MgCa(SiO3)2  Iron  is  usually  present  in  small  amounts,  described 
p.  506. 

This  mineral,  a  member  of  the  group  of  monoclinic  pyroxenes  occasionally  occurs 
in  transparent  specimens  worthy  of  cutting.  Light  to  dark  oily  leaf  green  or  bottle 
green. 

OCCURRENCE  OF  CUTTING  MATERIAL. — Light  green  crystals  in  Ala  Piedmont 
and  DeKalb.  N.  Y.  Dark  green  crystals  from  Zillerthal,  Tyrol. 

ENSTATITE. — (Mg.Fe)SiOs,  described  p.  504,  is  now  found  as  transparent  green 
material  accompajiying  the  diamonds  in  South  Africa  and  is  cut  in  facetted  stones 
and  sold  as  the  Cape  green  garnet. 

BPIDOTE.— CaaAl«(AlOH)(SiO4)3,  described  p.  528,  is  of  a  peculiar  shade  of  yel- 
lowish green,  similar. to  that  of  the  pistachio-nut  By  transmitted  light  in  directions 
at  right  angles  the  stone  will  appear  respectively  green  and  brown,  by  reflected  light 
Is  nearly  black. 

Bauer  states  only  one  locality  furnishes  material  which  is  transparent  enough 
to  be  worth  cutting,  namely,  Knappenwand,  Untersulzbachthal,  Tyrol. 

PREHNITE. — H2CaoAl2(SiO4)3.  This  mineral  described  p.  535,  occurs  in  Nama- 
qua  land  in  beautiful  crystals  which  furnish  green  stones  like  chrysolite  and  others 
resembling  chrysoprase.  The  material  from  the  many  other  localities  is  only  trans- 
lucent and  little  used. 

MOLDAVITE. — A  green  glass  found  in  Bohemia  and  Moravia  and  resembling 
green  bottle  glass,  was  long  suspected  to  be  the  product  of  old  and  forgotten  glass 
factories. 

The  finding  of  the  same  material  deep  down  in  the  garnet  mines  of  northern 
Bohemia  show  that  it  far  antedates  man  and  the  present  supposition  is  that  the 
fragments  are  glassy  bombs  due  to  the  bursting  of  a  meteorite  which  fell  in  near  the 
end  of  the  Tertiary  period. 

GARNET.-  -Demantoid,  Almandine,  Etc.     Described  on  p.  509. 

COMPOSITION.— R"3R"'2(SiO4)3.  R"  is  Ca,  Mg,  Fe  or  Mn. 
R'"  is  Al,  Fe'"  or  Cr,  rarely  Ti. 

GEM  VARIETIES  AND  THEIR  OCCURRENCE. 

DEMANTOID,  so  called  from  its  diamond  like  lustre  and  fire  is  the  most  highly 
valued  garnet.  It  is  also  called  olivine  and  uralian  emerald,  and  is  a  variety  of 
andradite,  Ca$Fe2(SiO4)3,  of  an  emerald  green  to  olive  green  color  (more  yellow  than 
the  true  emerald)  with  brilliant  lustre  and  the  greatest  color  dispersion  (fire),.  057, 
known.  Its  index  is  very  high,  1.88  to  1.89,  but  it  is  soft,  6  to  6.5 

It  is  found  in  the  Sissersk  district,  western  side  of  the  Urals  and  in  Piedmont. 

ESSONITE  or  Hessonite,  reddish  brown  to  orange,  CINNAMON  STONE  golden 
yellow  to  brown,  and  HYACINTH  or  false  hyacinth,  golden  yellow,  are  all  essentially 
alike  and  are  of  the  general  formula  CasAhtSiO^s.  They  are  somewhat  softer  than 


568  MINERALOGY. 

other  garnets,  7,  but  take  a  good  polish  and  are  more  brilliant  by  artificial  light. 
A  peculiar  granulated  appearance  under  the  glass  is  very  characteristic. 

The  best  are  from  the  Ceylon  gravels,  also  found  at  San  Diego  Co.,  California,  and 
formerly  in  Switzerland. 

ALMANDINE,  known  also  as  Syriam  garnet,  Adelaide  ruby,  and  Siberian  garnet, 
is  violet,  reddish  violet,  crimson  and  brownish  red.  It  loses  brilliancy  in  artificial 
light  and  was  formerly  much  used  cut  "cabochon."  It  is  remarkable  for  its  char- 
acteristic absorption  spectrum  and  is  of  the  type  FesAhCSiO^s. 

Formerly  from  Alabanda,  Asia  Minor,  whence  the  name.  Various  parts  of  India 
and  Burmah,  Brazil,  Uruguay,  Australia,  U.  S.  A.,  German  East  Africa. 

RHODOLITE. — A  rose  pink  variety  from  Macon  Co..  N.  C.,  equivalent  to  two 
molecules  pyrope  to  one  of  almandine. 

PYROPE,  the  most  used  garnet,  is  also  known  by  many  misleading  names,  like 
Cape  ruby,  Colorado  ruby,  while  not  a  clear  transparent  stone  often  occurs  fire  red 
and  blood  red.  Light-colored  stones  backed  by  colored  glass  constitute  the  fire 
doublets.  It  is  of  the  type  Mg3Al2(SiO4)3. 

Occurs  in  enormous  quantities  in  Bohemia  near  Teplitz  as  small  red  stones  with 
tinge  of  yellow.  Also  in  the  "blue  ground"  of  the  diamond  mines  at  Kimberley,  and 
in  Arizona,  Colorado,  Australia,  Rhodesia,  etc. 

SPESSARTITE  of  the  type  Mn3Al2(SiO4)3  has  furnished  a  few  very  fine  stones; 
it  is  more  brilliant  than  hyacinth  and  of  a  peculiar  brownish  red  color. 

Occurs  at  Spessart,  Germany,  Ceylon  and  Amelia  Co.,  Va. 

PHYSICAL  AND  OPTICAL  CHARACTERS  OF  GARNETS. 

SPECIFIC  GRAVITY. — 3.55  to  4.20  or,  by  varieties,  essonite,  3.6-3.7;  pyrope,  3.7- 
3.8;  rhodolite,  3-79-3-87;  almandine,  3.9-4.2;  spessartite,  4-4.3;  demantoid,  3.85. 

HARDNESS. — A  little  harder  than  quartz.  Essonite,  7  +  ;  pyrope,  7  +  ;  rhodolite, 
7  +  ;  almandine,  7.5;  spessartite,  7.5-8;  demantoid,  6.-6.5. 

LUSTRE. — Vitreous  but  takes  good  polish.  The  lustre  of  essonite  is  more  brilliant 
by  artificial  light.  On  the  other  hand,  almandine  loses  brilliancy. 

REFRACTION  AND  INDICES  OF  REFRACTION. — Singly  refracting  and  yet  practically 
always  with  some  local  double  refraction  giving  between  crossed  nicols  every  90° 
gradual  transitions  from  light  to  darkness.  Essonite,  1.75-1.78;  pyrope,  1.75-1.78; 
rhodolite,  1.76;  almandine,  1.77-1.81;  spessartite,  1.79-1.81;  demantoid,  1.88-1.89. 

COLOR  DISPERSION. — Essonite,  .028;  pyrope,  .027;  almandine,  .024;  demantoid, 
•057- 

ABSORPTION  SPECTRUM. — Almandine  and  rhodolite  show  lines  corresponding  to 
wave-lengths  570  to  585  and  510-495. 

ACTION  X-RAYS. — Essonite  almost  unpenetrated. 

QUARTZ.— Amethyst,  Citrine,  Etc.     Described  on  p.  484. 
COMPOSITION. — SiO2. 

COLOR   VARIETIES  AND   THEIR   OCCURRENCE. 

ROCK  CRYSTAL. — Colorless  and  water  clear.  The  crystallus  of  the  ancients, 
from  the  idea  that  it  was  ice  permanently  frozen.  It  was  made  into  drinking  cups 
and  solid  finger  rings  for  the  Romans,  and  balls  of  crystal  were  carried  in  the 
hands  for  coolness  and  used  also  as  a  lens  for  cauterizing  and  for  kindling  fire. 


MINERALS   USED  AS  PRECIOUS  STONES.  569 

At  present  rock  crystal  is  cut  into  imitation  diamonds,  such  as  Lake  George, 
Bristol,  Irish,  etc.,  diamonds.  The  chief  localities  are  Sierra  do  Cristaes,  Brazil, 
Madagascar  and  Switzerland,  others  are  France,  Hungary 

AMETHYST,  from  a  Greek  word  meaning  "wineless,"*  is  purple  to  violet,  often 
irregularly  diffused.  "The  rosy  hue  shining  out  from  the  purple."  It  is  less  bril- 
liant by  candle  light. 

Amethyst  invariably  shows  on  fracture  curious  ripple  marks,  due  to  the  fact 
that  it  is  always  composed  of  alternating  right-  and  left-handed  crystals. 

Up  to  1600  and  even  in  the  nineteenth  century  it  kept  a  high  rank.  "Queen  Char- 
lotte's necklace,  valued  at  $10,000,  would  possibly  now  be  valued  at  $500.00." 

Fine  amethysts  come  from  Rio  Grande  do  Sul,  Brazil,  and  from  Uruguay  and 
Siberia.  Other  localities  are  numerous,  such  as  Ceylon,  India,  N  C  ,  Ga.,  Penn. 
In  preparing  for  market  the  poorer  colored  portions  are  chipped  from  the  pebbles 
and  crystals  and  the  fine-colored  bits  selected  and  sold. 

CITRINE,  from  citron,  alluding  to  the  brownish-yellow  to  yellow  color,  is 
commonly  called  by  jewelers  topaz.  Much  of  the  yellow  quartz  sold  is,  however, 
burnt  amethyst  or  burnt  smoky  quartz.  It  is  chiefly  from  Brazil. 

CAIRNGORM,  from  the  locality  Cairngorm,  in  Scotland,  is  often  sold  as  Scotch 
topaz. 

SMOKY  QUARTZ. — The  Spanish  variety  from  Sierra  Morena,  Spain,  turns 
yellow  on  heating  and  is  sold  as  Spanish  topaz.  "Alengon  diamonds"  were  smoky 
quartz. 

ROSE  QUARTZ,  named  from  its  color,  is  not  found  in  crystals.  The  best  comes 
from  South  Dakota,  Paris,  Me.,  Katonah,  N.  Y.  Other  localities  are  Madagascar, 
Bavaria  and  Urals.  Sometimes  called  Bohemian  ruby. 

VARIETIES   DUE  TO  INCLUSIONS  OR  STRUCTURE  AND  THEIR 
OCCURRENCE. 

PRASE  OR  MOTHER  OF  EMERALD.— Originally  a  pale  green  stone,  colored 
by  included  leek  green  fibres  of  actinolite  and  supposed  at  one  time  to  be  the  matrix 
of  the  emerald.  It  was  valued  because  it  was  supposed  to  possess  the  powers  of  the 
emerald  to  a  less  degree  (for  instance,  to  lose  its  color  on  contact  with  poison). 

Although  the  ancient  locality  is  unknown  it  occurs  at  Halbachtal,  Salzburg, 
Breitenbunn,  Saxony,  Finland  and  Scotland. 

AVENTURINE  QUARTZ. — The  name  from  "Aventura" — an  accident — was 
first  applied  to  a  glass  produced  by  accidentally  spilling  copper  filings  into  the 
melted  glass.  This  material,  now  sold  as  goldstone,  is  somewhat  similar  to  quartz, 
containing  spangles  of  mica,  hematite,  etc.  The  favorite  colors  are  golden  brown, 
reddish  and  greenish.  The  green  from  the  Altai  Mts.  is  much  valued  in  China. 

STAR  QUARTZ.  —  Showing  a  six-rayed  star.  Usually  massive  rose  or  milky 
quartz. 

CAT'S  EYE. — Translucent  greenish  or  greenish  gray  due  to  asbestos. 

Chiefly  from  Ceylon  and  India  and  an  inferior  grade  from  Fichtelgebirge,  Bavaria. 

*  Pliny  states:  "The  lying  Magi  hold  that  these  gems  are  an  antidote  to  drunken- 
ness and  take  their  name  from  this  property,"  and  then  he  suggests  the  name  to 
have  been  given  because  the  color  approximated  but  did  not  reach  wine  color.  King 
suggests  the  word  is  a  corruption  of  the  Persian  word  Shimest* 


570 


MINERALOGY. 


It  is  imitated  by  "bleached  "  tiger's  eye.  It  was  a  valued  specific  for  croup,  sore  eyes, 
colic,  and  other  troubles. 

TIGER'S  EYE  AND  FALCON'S  EYE. — There  was  found  in  Griqualand,  West 
South  Africa,  large  quantities  of  an  altered  fibrous  mineral,  crocidolite,  consisting 
chiefly  of  quartz.  While  sold  originally  as  crocidolite  it  is  now  sold  as  tiger's  eye  if 
tawny  yellow  in  color  and  as  falcon's  eye  when  deep  blue  in  color. 

A  similar  but  paler  blue  altered  crocidolite  from  Salzburg,  Austria,  is  called  siderite 
or  sapphire  quartz. 

DUMORTIERITE  QUARTZ.— Is  cut  from  the  California  and  Arizona  localities. 


ANDALUSITE.  Composition.  AhSiOs.  Described  p.  518.  Transparent  var- 
ieties are  remarkable  for  strong  pleochroism  and  for  a  red  color  visible  from  the  in- 
terior in  addition  to  the  brown  or  green  body  color. 

Optical  Characters. 

Biaxial  (— ),  y,  1.643;  a,  1.632;  7  —  a,  .on.  Strongly  pleochroic.  Brown 
shows  reddish  brown  and  greenish  yellow.  Green  shows  olive  green,  yellow  and  red. 

Occurrence. — Good  stones  are  found  at  Minas  Novas,  Minas  Geraes,  Brazil, 
and  in  the  gem  gravels  of  Ceylon. 

AXINITE. — A  borosilicate  of  .calcium  and  aluminum. 

Triclinic  in  acute  wedge-shaped  (axe-shaped)  crystals.  The  triclinic  symmetry 
very  evident,  Fig.  5.  The  colors  are  clove  brown  to  smoky  violet,  sometimes 
cherry  red,  and  the  lustre  a  strong  vitreous  which  takes  a  good  polish. 

OPTICALLY  biaxial  (— )  with  y  =  1.68,  a  =  1.67,  y —  a  =  .009,  and  strong 
pleochroism,  giving  violet,  green  and  brown. 

BEFORE  BLOWPIPE,  ETC. — Violet  changes  to  brown,  then  becomes  colorless. 
Fuses  easily.  Gives  green  flame  of  boron.  Insoluble  in  acid,  but  gelatinizes  after 
fusion. 

OCCURRENCE. — Violet  crystals  from  Roseberry,  Tasmania.  Brown  to  red  crystals 
from  Bourg  d'Oisans,  Dauphiny.  Reported  from  San  Diego  Co.,  Cal. 

Other  minerals  occasionally  cut  as  transparent  stones  are 
staurolite,  chondrodite,  datolite,  various  zeolites,  fluorite,  apatite, 
piedmontite,  cancrinite,  willemite,  cassiterite. 

B.    THE  TRANSLUCENT  TO    OPAQUE   STONES. 
TURQUOIS.— Turkis  or  Turkish  Stone.* 

COMPOSITION.— Al2(OH)3PO4.H2O  and  always  contains  some 
copper  and  iron  which  give  it  color. 

GENERAL  DESCRIPTION.— Sky  blue  to  green  opaque  nodules  or 
veins,  also  in  rolled  masses. 

In  general  not  crystalline  but  apparently  colloidal  and  somewhat  porous.  It  is 
the  only  opaque  stone  which  ranks  as  a  precious  stone,  and  was  the  Callais  of  Pliny 
which  "resembled  Lapis  Lazuli  but  whiter  and  of  the  hue  of  the  sea  where  it  is 
shallow." 

*  The  gem  came  from  Persia  to  Europe  by  way  of  Turkey. 


MINERALS    USED   AS  PRECIOUS  STONES.  571 

It  has  always  been  the  favorite  stone  in  Persia  and  in  Europe  in  the  middle  ages 
it  was  most  popular,  the  preference  being  for  the  greener  shades. 

Physical  Characters. 

SPECIFIC  GRAVITY. — 2.75  to  2.89.  Los  Cerillos,  2.71  to  2.82. 
Surface  stones,  2.42  to  2.65. 

HARDNESS. — Less  than  6. 

LUSTRE. — Dull  and  wax-like  but  takes  a  good  and  fairly  durable 
polish. 

COLOR. — Sky  blue  to  greenish  blue  or  when  iron  prevails,  yellow- 
ish green  to  apple  green  or  pea  green.  The  colors  are  more  blue 
in  artificial  light  than  daylight.  All  fade  in  time,  and  the  color 
is  injured  by  perspiration,  grease,  liquids  anu  heat. 

Optical  Characters. 

Index  of  refraction  about  1.6 1.     Not  penetrated  by  X-rays. 

BEFORE  BLOWPIPE,  ETC. — Infusible  but  colors  the  flame  green. 
In  closed  tube  cracks,  flies  to  pieces,  yields  water  and  becomes 
brown.  Soluble  in  hydrochloric  acid,  the  solution  becoming  fine 
blue  with  ammonia. 

REMARKS. — A  secondary  phosphate  due  to  action  of  phosphate  solutions  on 
aluminous  material. 

The  best  stones  still  come  from  eastern  Persia  near  Nishapur  in  seams  in  a 
brecciated  trachyte.  Inferior  specimens  come  from  Asia  Minor  at  Serbal  in  Sinai 
Peninsula,  Turkestan  and  Kirghiz. 

Ancient  Aztec  workings  exist  near  Los  Cerrillos,  New  Mexico,  and  good  stones 
were  obtained  near  these  at  Turquois  Hill.  Other  old  workings  in  San  Bernardino 
Co.,  Calif.,  yielded  pale  colored  stones  and  Nevada,  Nye  Co.,  yields  a  dark  sky  blue 
to  pale  blue.  Often  mottled  or  "turtle  back"  material.  Arizona,  Colorado,  Mexico 
also  have  yielded  material. 

IMITATIONS    OF  TURQUOIS   AND    SIMILAR   STONES. 

Turquois  can  be  colored  by  placing  in  a  solution  of  Berlin  blue  under  an  air  pump 
and  exhausting  the  air.  Turquois  colored  by  Berlin  blue  is  grayish  blue  by  artificial 
light  and  changes  color  in  ammonia. 

By  precipitating  the  proper  proportions  of  hydrous  phosphate  of  aluminum  and 
copper  phosphate  and  pressing  hydraulically  while  still  wet  a  product  can  be  made 
equal  or  superior  in  color  to  natural.  Slight  differences  of  hardness,  specific  gravity 
and  indices  of  refraction  exist  but  the  principal  distinctions  are  that  if  heated 
real  turquois  splinters,  flies  to  pieces  and  turns  brown,  and  synthetic  turquois  fuses 
quietly  to  a  black  glass.  In  water  synthetic  turquois  becomes  deeper  blue  and 
the  surface  shows  many  little  cracks. 

ODONTOLITE  OR  BONE  TURQUOIS. — In  the  vicinity  of  Simor,  Lower 
Languedoc,  France,  are  found  numerous  (ossil  teeth  and  bones,  of  the  mastodon  and 
dinotherium,  which  have  taken  up  phosphate  of  iron  and  become  bluish  gray  in 


572 


MINERALOGY. 


color  but  on  heating  become  a  beautiful  blue.  Occasionally  also  they  are  found 
colored  green  by  copper  salts.  Some  similar  material  found  in  Siberia  is  also  blue 
colored. 

The  material  strongly  resembles  turquois,  but  differs  from  it  in  that  its  color 
by  candle  light  is  dull  and  gray;  under  the  microscope  the  organic  structure  is  evi- 
dent; it  effervesces  when  touched  with  acid,  and  it  yields  a  bad  smell  on  ignition. 

CHRYSOCOLLA,  p.  372,  is  rarely  cut  unless  contained  in  some  harder  substance 
like  quartz  or  chalcedony.  Occasionally  translucent  blue  and  bluish  green  specimens 
are  cut.  It  has  an  enamel-like  texture  and  some  blue  specimens  resemble  turquois. 

VARISCITE. — A1PO42H2O  in  bright  green  to  bluish  green,  compact,  opaque, 
rounded  masses  and  veins  resembling  turquois  and  suitable  for  cutting. 

It  may  be  the  oldest  gem.*  It  is  found  in  Cedar  Valley,  Utah  and  in  several 
parts  of  Nevada. 

LAZUXITE. — Blue  Spar.  A  complex  phosphate  of  aluminum  and  other  bases. 
The  massive  material  is  sometimes  cut  and  could  readily  be  mistaken  for  turquois. 
In  Germany  it  is  known  as  "Blauspat." 

The  principal  occurrences  are  Kriglach,  Styria;  Werfen,  Salzburg;  Zermatt. 
Tyrol;  Sinclair  Co.,  N.  C.,  and  Graves  Mt.,  Ga. 

SMITHSONITE. — ZnCO3  described  on  p.  300. 

The  sacred  stone  of  the  Aztecs  "Chalchihuitl,"  long  supposed  to  have  been 
turquois,  is  now  thought  to  be  the  beautiful  banded  azure  blue  smithsonite  of  the 
Ysabelita  mine,  Mexico.  Green  smithsonite  occurs  at  the  same  mine. 

OPAL.     Described  on  p.  487. 

COMPOSITION. — Si02.wH2O,  (H2O,  5  to  12  per  cent.).  "Made 
of  the  glories  of  the  most  precious  gems,"  "fairest  and  most 
pleasing  of  all  jewels"  is  Pliny's  description  of  opal.  The  beauty 
is  due  not  to  the  color  of  the  stone  but  to  varying  brilliant  inter- 
ference colors,  produced  by  thin  films  of  air  or  of  other  opal  in 
the  cracks  developed  during  the  drying  of  the  original  jelly- 
like  mass. 

On  the  basis  of  color  of  the  stone  opals  are  broadly  divided  by  jewelers  into: 

WHITE  OPALS,  colorless,  milky  yellowish  and  other  light  tints. 

BLACK  OPALS,  dark  gray,  blue  and  nearly  or  quite  black. 

FIRE  OPALS,  reddish  or  orange  colored. 

Many  names  have  been  used  based  on  the  predominance  of  one  or  the  other  inter- 
ference color;  these  are  little  used  now.  An  example  is  harlequin  opal,  with  the 
interference  colors  in  small,  regular  angular  patches  of  every  hue. 

In  others  some  peculiarity  in  structure  is  the  basis  of  a  name. 

*  There  was  found  in  an  Old  Celtic  grave  at  Mane  er  Hrock  in  Brittany  a  con- 
siderable number  of  rounded  beads  from  the  size  of  naxseed  to  that  of  a  pigeon's  egg, 
from  apple  to  emerald  green  in  color,  and  often  necked  with  white  or  blue.  The 
composition  is  close  to  variscite.  The  remarkable  thing  is  that  they  are  more  trans- 
parent, and  of  more  beautiful  colors  than  any  specimens  found  elsewhere. 


MINERALS   USED  AS  PRECIOUS  STONES.  573 

HYDROPHANE. — The  cracks  being  filled  with  air  fail  to  give  play  of  color 
but  if  filled  with  a  denser  medium,  by  dropping  in  water  the  colors  appear. 

CACHOLONG,  a  milky  white  almost  opaque  variety,  which  adheres  to  the 
tongue. 

GIRASOL. — Almost  transparent  but  with  a  wave  of  blue  light,  something  as  in 
moonstone. 

OCCURRENCE. — The  ancient  source  of  the  best  is  said  to  have  been  India.  No 
such  gem  comes  from  there  now.  The  mines  in  Hungary  near  Czernovitza  yielded 
much  slightly  yellowish  opal  and  some  fine,  and  were  long  the  only  important  source. 

In  the  early  eighties  the  rich  blue  opals  were  discovered  in  Queensland,  Australia, 
in  thin  veins  through  a  brown  jasper,  and  a  little  later  bright  yellowish  opals  were 
found  in  pipes  of  jasper  in  a  sandstone  rock  in  West  Queensland. 

In  1889  white  opals  of  fine  quality  were  found  at  White  Cliffs,  New  South  Wales, 
in  Cretaceous  rocks  replacing  other  minerals,  bones  and  wood,  and  filling  cavities. 
In  ten  years  these  were  exhausted.  In  1904  at  Lightning  Ridge,  New  South  Wales, 
the  dark-colored  so-called  black  opals  were  found  in  essentially  the  same  formation 
as  at  White  Cliffs.  These  also  are  practically  exhausted. 

Mexico  yields  many  fire  opals  and  some  white  opals  which  are  sometimes  facetted, 
sometimes  cut  with  matrix.  They  are  more  translucent  than  other  opals  and  are 
said  to  lose  their  play  of  colors. 

In  Humboldt  County,  Nevada,  opalized  wood,  often  of  dark  color  but  with 
beautiful  play  of  colors  is  found.  It  has  a  tendency  to  crack  during  and  after  cutting. 

CHALCEDONY.— Carnelian  Onyx,  Etc.     Described  on  p.  486. 

COMPOSITION. — Silica  with  occasionally  a  little  water.  The 
earlier  gems  were  engraved  rather  than  cut  and  no  substance  has 
proved  as  suitable  or  durable  as  chalcedony.  Before  the  coming  of 
the  sapphires  and  other  transparent  gems  from  India  and  Ceylon, 
carnelian  and  onyx  were  much  used  by  the  Romans  and  through 
the  Renaissance  period  for  seals  and  cameos.  The  beeswax  then 
used  did  not  stick  to  it.  "Signeth  very  faire  without  any  of  the 
wax  sticking  to  it." 

A  pale  blue  variety,  sapphirine,  was  used  much  earlier  in  Baby- 
lonian and  Persian  cylinders  and  Etruscan  scarabs. 

The  best  known  varieties  are: 

CHALCEDONY  or  Girasol,  white,  gray  and  "  tendon  "  color. 

CARNELIAN. — To  the  Romans  dull  brick  red  and  little  value,  now  the  name 
for  clear  red. 

SARD. — To  the  Romans  the  bright  clear  red  now  the  name  for  brownish-red. 

CHRYSOPRASE  (golden  leek),  an  apple  green  variety,  colored  by  nickel. 

BLUE  CHRYSOPRASE.     Chalcedony  containing  chrysocolla. 

BLOODSTONE  OR  HELIOTROPE.  Deep  leek  green  with  spots  of  red  jasper. 
Said  to  have  been  used  as  a  mirror  in  detecting  solar  eclipses.  Much  used  in  the  Byzan- 
tine period  for  sacred  carvings,  the  red  jasper  being  said  to  be  the  Savior's  blood. 


574  MINERALOGY. 

AGATE. — Variegated  chalcedony  in  clouds,  bands,  spots  or  layers.  Named 
for  the  river  Achates  in  Sicily. 

MOSS  AGATE  AND  MOCHA  STONE,  with  moss-like  inclusions. 

ONYX. — Originally  oriental  alabaster,  later  the  tricolored  agate  used  for  signet 
rings.  Pliny  says  "a  white  mark  on  sard  like  the  human  nail  placed  upon  flesh 
and  both  of  them  transparent." 

The  tricolored  agate  was  cut  across  parallel  layers  so  as  to  give  two  bands  of 
dark  brown  with  a  layer  of  colorless  transparent  between.  This  was  long  the  favorite 
signet  stone. 

Onyx  to-day  is  an  agate  with  regular,  even  planes  of  different  colors,  especially 
white  and  black  or  white,  brown  and  black,  and  was  used  much  for  cameos. 

SARDONYX.  Onyx  with  one  of  the  layers  of  sard.  Pliny's  perfect  sardonyx 
was  base  black  or  chocolate;  middle  opaque,  fatty  white;  surface  brown  or  red. 

OCCURRENCE. — India  is  noted  for  its  fine  carnelians  and  agates.  Brazil  furnishes 
the  "carnelian"  so-called  free  from  iron,  which  is  colored  and  polished  at  Idar* 

Uruguay  furnishes  much  material  and  agate  and  chalcedony  are  found  in  a  great 
many  localities  in  America,  such  as  Agate  Bay,  Lake  Superior,  Colorado  and  through 
the  Rocky  Mountains.  Agatized  wood  comes  from  Arizona.  Chrysoprase  from 
Venus  Hill,  California,  and  Blue  Chrysoprase  from  Globe,  Arizona. 

JADE.f 

The  great  "  Nephrit-Frage "  arose  because  jade  weapons  apparently  composed 
of  Asiatic  jade  were  found  in  many  parts  of  Europe,  and  no  localities  for  raw  jade 
were  known.  More  careful  search  found  raw  jade  in  Silesia,  Siberia,  Italy,  and 
elsewhere. 

Possibly  only  because  its  toughness  made  jade  suitable  for  delicate  carving  and 
possibly  from  superstition,  China  and  Japan  and  to  some  extent  India  and  ancient 
Mexico  grew  to  value  the  jade  beyond  other  stones  and  to  carve  from  it  with  im- 
mense labor  vessels,  figures,  beads  and  amulets.  The  plundering  of  China  has 
brought  many  of  these  to  Europe  and  America. 

In  Europe  in  the  early  part  of  the  seventeenth  century  it  was  enormously  valued. 
Deboot  says  a  piece  no  larger  than  a  thaler  sold  for  100  pounds.  This  seems  to 
have  been  due  to  the  powerful  medicinal  properties  attributed  to  it.  Both  worn 
as  an  amulet  and  administered  as  a  powder,  it  was  held  to  cure  kidney  troubles. 

In  1863  Damour  showed  that  while  most  of  the  light-colored 
jade  objects  were,  as  supposed,  the  variety  nephrite  of  the  mineral 
amphibole,  many  of  the  more  valued  green  jades,  though  much 

*The  white  chalcedonies  formerly  found  at  Idar  and  the  so-called  Brazilian 
carnelian  now  worked  there  are  free  from  iron.  They  are  therefore  easily  given 
other  colors  by  different  solutions  and  processes,  the  colors  including  black,  sard 
brown,  sard  onyx,  lemon  yellow,  blue,  deep  blue,  green. 

t  Jade  for  various  reasons  has  an  extensive  literature  and  has  been  more  valued 
by  various  races  and  for  more  various  reasons  than  perhaps  any  other  stone.  In 
the  Stone  Age  the  man  with  the  tough  jade  weapon  was  master  of  the  man  with 
weapons  of  any  other  material,  and  jade  weapons  were  valued  and  sought  for  with 
a  care  not  since  equaled. 


MINERALS   USED   AS  PRECIOUS  STONES.  575 

like  nephrite  in  toughness  and  translucency,  were  of  a  totally 
different  composition  and  were  definitely  harder  and  heavier. 
To  these  he  gave  the  name  jadeite  and  a  third  name  chloromelanite, 
essentially  a  jadeite  rich  in  iron.  In  these  the  constant  characters 
were  extreme  toughness,  lack  of  brilliancy  and  in  general  trans- 
lucency, and  the  dominant  color  was  from  white  to  green.  Al- 
though two  distinct  minerals,  it  has  seemed  most  convenient  to 
discuss  them  as  if  varieties  of  one  substance,  broadly  called  jade. 

COMPOSITION. — Nephrite  Ca(MgFe)3(SiO3)4,  Jadeite  Na2Al<r 
(Si03)4. 

NAME. — Jade  is  from  the  Spanish  hijada  =  kidney.  Nephrite 
is  the  Latin  word  for  kidney.  Jadiete  is  Damour's  name  for  the 
new  species  discovered  by  him  among  the  jades. 

SPECIFIC  GRAVITY. — Nephrite  2.97  to  3.18,  the  lighter  colored 
being  the  lower  specific  gravity.  Jadeite  3.3  to  3.35,  but  lower 
when  altered. 

HARDNESS. — Nephrite  5.5,   Jadeite  6  to  7. 

TOUGHNESS. — Nephrite  very  difficult  to  break.  Jadeite  equally 
tough  when  fine  fibrous,  less  so  when  granular. 

COLORS. — Nephrite:  Turkestan,  yellowish  gray  to  white  or 
greenish;  Silesia,  dark  green  to  bluish  green;  New  Zealand,  dark 
green;  Alaska,  dark  green  to  nearly  black.  Jadeite:  Burma>  white, 
gray,  green,  brown  or  red,  often  with  streaks  of  emerald  green. 

LUSTRE. — Dull,  oily,  not  brilliant,  even  when  polished. 

CRYSTALLIZATION  AND  STRUCTURE.  —Both  are  monoclinic.  In 
nephrite  the  microscopic  crystals  are  confusedly  interlaced  fibres, 
which  in  the  New  Zealand  material  are  sometimes  coarser  and 
recognizable.  Jadeite  occurs  in  both  fine  fibrous  and  granular 
masses. 

CLEAVAGE. — Not  recognizable  except  in  thin  sections.  In 
nephrite  cleavages  of  54°  38'  have  been  detected.  In  jadeite 
cleavages  of  about  86°  have  been  detected. 

REFRACTION  AND  INDICES  OF  REFRACTION.- — Though  both  are 
doubly  refracting,  this  is  not  determinable  in  the  cut  stone. 
The  indices  average,  nephrite  about  1.6 1,  jadeite  about  1.67. 

ACTION  X-RAYS. — Nephrite  nearly  opaque. 

BEFORE  BLOWPIPE,  ETC. — Nephrite  is  unchanged  at  red  heat, 
but  fuses  at  4  to  a  colored  glass.  Jadeite  fuses  very  easily  (2.5) 


5  76  MINERAL  OGY. 

with  a  strong  yellow  flame  to  a  transparent  bubbly  glass.     Neither 
is  readily  attacked  by  hydrochloric  acid. 

OCCURRENCE. — Nephrite  occurs  in  great  masses  twenty  to  forty  feet  thick,  in 
gneiss,  in  Turkestan,  in  the  valleys  of  the  Karakash,  Yarkand  and  Kashgar  rivers. 
These  are  the  sources  of  most  of  the  light-colored  nephrite  with  specific  gravity  2.9 
to  3.  It  is  said  to  occur  in  several  provinces  in  China,  and  it  occurs  in  place,  in 
serpentine  on  D'Urville  Island,  New  Zealand,  and  also  as  numerous  boulders"  of  dark 
green,  light  green,  and  gray  color.  Other  occurrences  are :  as  boulders  near  Lake 
Baikal,  Siberia;  both  as  boulders  and  in  place  in  Silesia:  in  New  Guinea  and 
Alaska. 

Jadeite  is  found  as  boulders  and  with  albite  forming  light  colored  layers  in 
green  serpentine  in  Mogoung,  Upper  Burma.  The  serpentine  is  in  sandstone.  It 
is  nearly  all  sold  to  China  and  amounts  to  about  $250,000  per  year.  Jadeite  is  said 
to  occur  also  in  China  and  Thibet  and  to  have  been  found  in  place  in  Italy. 

JADE-LIKE    MINERALS. 

CALIFORNITE,  a  compact  variety  of  vesuvianite,  described  on  p.  511,  has  the 
appearance  of  a  jade  and  polishes  well.  It  is  found  in  Siskiyou  and  Fresno  Counties, 
California.  The  pieces  are  in  some  cases  as  much  as  5  feet  square  and  2  feet  thick, 
of  excellent  quality  for  polishing.  The  associated  rock  is  precious  serpentine. 

SERPENTINE. — H4Mg3Si2O9,  with  replacement  by  Fe.     Described,  p.  544. 

Although  a  soft  mineral  serpentine  takes  a  good  polish  and  is  durable  and  its 
frequent  occurrence  in  translucent  varieties  of  bright  oil  green  to  paler  green  resem- 
bling jade  and  the  ease  with  which  it  is  worked  has  resulted  in  its  very  extensive  use 
for  decorative  purposes,  art  work,  cameos,  intaglios,  etc.  At  Zoblitz,  Saxony,  it  is 
the  basis  of  a  large  industry. 

Special  varieties  are:  Williamsite,  apple  green,  nearly  transparent.  Bowenite 
or  Tangiwai,  rich  to  pale  green.  Satelite,  a  dull  green  fibrous  variety,  mixed  with 
chalcedony  and  cut  as  cat's  eye.  Green  stone  of  South  Africa,  malachite  green. 

Localities  are  very  numerous.  Snarum,  Norway;  Miask,  Urals;  Newburyport, 
Mass.;  Milford  Sound,  New  Zealand,  and  Smithfield,  R.  I.,  Texas,  Pa.;  Venus  Hill, 
Cal.  (satelite). 

LAPIS  LAZULI. 

This  stone,  the  sapphire  of  the  ancients  and  the  only  stone  of 
value  in  Egypt  at  the  time  of  the  early  Pharaohs,  is  not  a  mineral 
but  a  complex  of  calcite,  colored  by  three  blue  aluminum  silicates. 
One  lazurite,  an  ultramarine,  involving  sodium  sulphide,  one 
hauynite,  and  the  third  sodalite.  It  is  a  deep  blue,  sometimes 
purplish,  and  often  spangled  with  little  crystals  of  pyrite.  The 
Chilian  variety  is  a  yellower  blue  and  has  white  or  gray  flecks. 

OCCURRENCE.— The  Egyptians  are  said  to  have  had  mines  in  Ethiopia.  The  oldest 
known  mines  are  in  the  Kokseha  Valley,  Badakshan,  Afghanistan,  and  it  is  also  said 
to  occur  in  India  at  Sadmoneir  and  Bijour.  Other  localities  are  Lake  Baikal,  near 
the  source  of  the  Koultouk;  the  Chilean  Andes,  and  Thibet. 


MINERALS   USED   AS  PRECIOUS  STONES.  577 

IMITATIONS   OF   LAPIS   LAZULI  AND   SIMILAR   STONES. 

IMITATIONS. — The  best  is  a  jasper  from  Nunkirk,  stained  blue.  It  is  called 
German  lapis  and  perfectly  imitates  the  Chilean,  but  fades  in  time. 

AZURITE,  p.  371,  is  sometimes  used  as  an  imitation.    It  is  the  same  color  but  softer. 

OCCURRENCE. — Material  suitable  for  cutting  is  found  in  many  localities:  Urals, 
Australia,  Chile,  Arizona,  California. 

SODALITE,  p.  500,  mentioned  as  forming  part  of  lapis  lazuli,  occurs  also  separa- 
tely and  is  sometimes  cut  cabochon  and  has  a  limited  use.  In  Bolivia  it  was  used 
by  the  aborigines  cut  pearl  shaped.  It  rarely  has  the  fine  blue  lapis  color. 

OCCURRENCE. — In  dense  masses  at  Dungannon,  Hastings  County,  Ont.,  Canada, 
and  at  Litchfield,  Maine.  In  translucent  material  in  Greenland;  Siebenburgen  and 
Vesuvius. 

FELDSPAR. — Moonstone,  Amazonite,  Etc.     Described  on  p.  488. 

COMPOSITION. — The  group  is  considered  to  consist  of  three 
distinct  species  and  a  number  of  intermediate  "isomorphous 
mixtures." 

Orthoclase  KAlSisOs  Monoclinic 

Albite  NaAlSiaOs  Triclinic 

Anorthite  CaAl2Si2O8  Triclinic 

Although  constituting  about  one  half  of  the  known  crust  of  the  earth  this  group 
of  great  species  only  occasionally  furnishes  material  suitable  for  jewelry. 

MOONSTONE. 

"Colorless,  diffusing  brilliant  rays  in  a  circle  after  the  fashion  of  that  luminary." 
The  only  variety  valued  in  jewelry.  Chiefly  a  variety  of  orthoclase,  but  also  of 
albite  or  intermediate  mixtures.  The  milky,  bluish  opalescence  from  which  they 
take  their  name  is  caused  by  inclusions,  which  lie  about  perpendicular  to  one  of  the 
cleavages. 

They  are  always  cut  more  or  less  steeply  en  cabochon  and  go  well  as  a  border 
for  large  colored  stones. 

OCCURRENCE. — At  the  present  day  practically  all  the  moonstones  on  the  market 
come  from  the  interior  of  Ceylon.  Formerly  many  came  from  the  St.  Gothard 
district  in  Switzerland.  Beautiful  stones  with  blue  opalescence  come  from  California. 
Other  localities  are  Amelia  Court  House,  Va.,  Rio  de  Janeiro,  Brazil,  and  West 
Australia.  Albite  moonstone  is  found  at  Media,  Penn. 

Peristerite  is  a  less  transparent  variety  from  Macomb,  N.  Y.,  and  Bathurst, 
Canada,  which  shows  a  pigeon  blue  opalescence. 

AMAZONITE  OR  AMAZON  STONE.— This  is  a  green  opaque  variety  of 
the  potash  feldspar  microcline. 

The  most  valued  variety  is  apple  green  in  color;  the  brighter  green  and  the 
varieties  with  streaks  and  flecks  of  white  yellow  or  red  are  of  little  worth. 

The  principal  localities  are  in  the  Ilmen  Mountains,  Orenburg,  Russia,  Virginia, 
Pikes  Peak,  Col.,  and  in  North  Carolina. 

The  name  was  given  by  Spaniards  to  some  green  mineral  found  among  the  Indians 
dwelling  near  the  Amazon  River.  No  occurrence  of  Amazon  stone  there,  however, 
38 


578  MINERALOGY. 

has  been  found  and  there  appears  to  have  been  some  confusion  with  a  jade  or  similar 
stone. 

SUNSTONE  OR  HELIOLITE. — Sunstone  is  chiefly  a  variety  of  oligoclase,  but 
also  of  albite  and  contains  flakes  of  hematite  or  goethite  which  impart  a  spangled 
bronze  appearance.  The  colors  vary  from  grayish  white  to  reddish  gray,  and  the 
material  resembles  aventurine  quartz  and  is  sometimes  called  aventurine  feldspar. 

Bauer  states  that  this  variety  of  feldspar  around  1800  was  very  rare  and  costly. 
Only  a  few  specimens  were  known  from  one  locality,  Sattel  Island  in  the  White  Sea. 

It  is  now  found  in  East  India,  Ceylon.  The  best  sunstone  is  from  Christiania 
fiord,  Norway.  Sunstone  almost  equal  to  the  Norwegian  is  found  at  Media,  Dela- 
ware County,  Penn.,  and  in  Amelia  Co.,  Va. 

LABRADORITE. — The  body  color  is  usually  a  dull  gray,  but  the  "interference" 
colors  which  come  and  go  as  the  stone  is  turned  from  side  to  side  are  usually  broad 
flashes  of  blue  and  green,  but  also  in  yellow,  red,  pearl  gray,  orange,  puce,  amber, 
and  peach-blossom  hues.  These  colors  are  due  both  to  a  regular  lamellar  structure 
and  to  regularly  placed  microscopic  inclusions. 

The  finest  specimens  are  brought  from  the  Isle  of  St.  Paul  off  the  coast  of  Labrador, 
but  other  localities  yield  beautiful  material,  Brisbane,  Queensland,  with  a  blue  schiller; 
Djamo,  Finland,  a  colorless  labradorite,  showing  the  interference  colors  in  concentric 
circles. 

MALACHITE.— Cu2(CO3)(OH)2.  Described  on  p.  371.  The  green  copper 
carbonate. 

Although  by  the  ancient  Greeks  and  Romans  the  easily  worked  malachite  was 
used  as  a  gem,  it  is  now  only  occasionally  so  used.  The  fine  fibrous  and  stalactitic 
varieties  are,  however,  used  in  large  quantities,  especially  in  Russia  at  Ekaterinenberg 
and  Petrograd  for  the  making  of  jewel  cases,  vases  and  even  table  tops  and  large 
columns.  In  general,  however,  the  articles  are  only  covered  with  a  thin  veneer  of 
the  malachite  made  from  comparatively  small  pieces  carefully  built  together  like  a 
mosaic. 

OCCURRENCE. — The  finest  malachite  is  found  in  large  masses  at  the  copper  mines 
of  Nizhni  Tagilsk  in  the  Ural  Mountains.  It  accompanies  the  copper  ores  in  many 
parts  of  the  world. 

CHLORASTROLITE  OR  ISLE  ROYALE  GREENSTONE,  from  chioros  (green), 
aster  (star),  and  lithos  (stone).  Small  rounded  pebbles  from  Isle  Royale,  Lake 
Superior,  which  are  opaque,  of  a  mottled  green  color,  somewhat  chatoyant  on  the 
rounded  sides,  and  take  a  high  polish. 

AMBER.— Succinite  Simetite. 

Amber  is  a  fossil  resin,  derived  from  a  now  extinct  variety  of 
pine  which  lived  during  the  Tertiary  period.  Its  composition  is: 
carbon,  78.96;  hydrogen,  10.51 ;  oxygen,  10.52.  It  consists  mainly 
(85  to  90  per  cent.)  of  a  resin  which  resists  all  solvents. 

PROPERTIES. — H.,  2.5.  Sp.  gr.,  1.065  to  1.081.  Lustre  resinous 
and  very  brilliant  after  polishing. 

The  color  is  yellow,  sometimes  reddish,  brownish,  and  whitish, 
often  clouded.  The  variety  from  Sicily,  simetite,  is  brownish  red 


MINERALS   USED  AS  PRECIOUS  STONES.  579 

with  a  beautiful  bluish  to  greenish  fluorescence.  Singly  refracting, 
though  often  locally  doubly  refracting.  Index  about  1 .54.  Nega- 
tively electrified  by  friction. 

While  the  Sicilian  amber  if  fluorescent  still  commands  a  high  price,  the  Prussian 
amber  is  sold  by  the  pound  and  used  for  mouthpieces  of  pipes,  cigar  and  cigarette- 
holders,  umbrella  handles  and  locally  cut  for  cheap  jewelry. 

It  formerly  ranked  very  high,  the  Greeks  obtained  it  from  the 
Teutonic  tribes  and  according  to  King,  is  entitled  to  "  the  highest 
antiquity  in  the  list  of  precious  stones  used  for  personal  ornament," 
since  Homer  mentions  no  gem  except  'the  gold  necklace  hung 
with  bits  of  amber/" 

It  is  obtained  now  as  for  over  2,000  years  chiefly  from  lignite-bearing  sandstone 
along  the  coast  of  the  Baltic  from  Danzig,  West  Prussia,  to  Memel,  East  Prussia. 
The  most  beautiful  is  obtained  off  shores  of  Catania,  Sicily. 

JET. — Jet  is  a  compact,  soft,  light  coal  of  a  lustrous  velvet  black  color,  suscep- 
tible of  a  high  polish. 

The  early  Britons  turned  it  on  the  lathe  into  rings,  bracelets,  anklets  and  later 
made  it  into  scarf  pins,  bracelets,  beads,  etc.,  and  in  Whitby,  Yorkshire,  there  is  still 
a  large  industry  amounting  to  about  $1,000,000  per  year. 

OCCURRENCE. — The  finest  specimens  are  now  found  in  detached  pieces  in  a  clay 
near  Whitby,  Yorkshire,  England.  It  also  occurs  in  Germany,  Colorado,  South 
France,  and  Aragon,  Spain. 

IMITATIONS. — In  this  country  it  has  been  displaced  by  black-colored  chalcedony. 
It  is  also  imitated  in  gutta  percha,  glass,  and  obsidian. 

ANTHRACITE  is  turned  into  compass  cases,  cups,  saucers,  vases,  candlesticks 
and  paperweights,  and  is  carved  by  hand  into  a  variety  of  small  ornaments.  Most 
of  the  anthracite  is  worked  at  Mountain  Top,  near  Glen  Summit,  Lucerne  County, 
Pa. 

RHODONITE. — MnSiOs.  Described  on  p.  271.  The  fine-grained  massive 
variety  is  often  cut  into  vases,  paper  weights,  and  in  rounded  stones  for  brooches,  etc. 
It  is  very  tough,  takes  a  good  polish  and  in  color  is  a  fine  rose  to  dark  red,  often 
attractively  veined  with  black. 

The  principal  localities  for  cutting  material  are  Cummington,  Mass  ,  and  Ekateri- 
nenberg,  Urals. 

THULITE  is  a  beautiful  rose  to  peach-blossom  red  variety  of  zoisite,  itself 
an  orthorhombic  epidote.  It  owes  its  color  to  a  little  manganese  and  is  essentially 
opaque. 

Fine  specimens  come  from  Telemark,  Norway,  and  Traversella,  Piedmont. 

HEMATITE.— Fe2O3.  Described  on  p.  271.  The  compact  brilliant  black 
variety  of  the  great  iron  ore  was  used  as  a  gem  by  the  Babylonians  and  Egyptians 
and  to  this  day  it  is  made  into  beads,  signet  stones,  bracelets,  etc.  When  cut  with 
a  dull  polish  it  is  very  similar  to  black  pearl. 

Other  translucent  or  opaque  stones  occasionally  cut  are:  thom- 
sonite,  lepidolite,  fuchsite,  hypersthene,  lodestone,  ilmenite, 
pyrite  and  rutile. 


PART  IV. 


DETERMINATIVE    MINERALOGY. 


CHAPTER  XXII. 

TABLES  FOR  RAPID  DETERMINATION  OF  THE  COM- 
MON MINERALS. 

All  schemes*  for  determining  minerals  utilize  essentially  the 
same  tests  and  differ  principally  in  the  order  in  which  they  are 
applied,  the  number  of  minerals  considered  and  the  completeness 
with  which  the  minor  or  confirmatory  tests  are  stated  in  the  scheme 
or  covered  by  a  reference  to  the  descriptions  of  the  minerals. 

The  tables  which  follow  are  in  the  main  an  elaboration  of  the 
tables  in  the  former  editions,  employing  essentially  the  same  classi- 
fying tests  but  differing  in  the  following  points: 

i°.  The  results  of  the  major  tests  are  summed  up  in  a  "KEY"  to 
59  numbered  groups. 

2°.  The  number  of  species  has  been  increased. 

3°.  The  groups  contain  tabulations  of  confirmatory  tests. 

4°.  In  the  thirty-five  groups  of  minerals  of  non-metallic  lustre 
alternative  tables  A  and  B  are  given,  A  the  physical  and  chemical 
tests,  B  the  tests  upon  crushed  fragments  with  the  polarizing 
microscope.  The  latter  have  proved  their  value  during  several 
years  of  use  as  auxiliary  tables  and  are  now  incorporated. 

*  They  may  be  said  to  vary  between  the  von  Kobell  (Brush-Penfield)  type  in 
which  "the  tables  have  been  so  developed  that  tests  for  characteristic  chemical 
constituents  furnish  the  chief  means  of  identification"  (preface  1898  edition  Brush- 
Penfield  Determinative  Mineralogy},  and  in  which  lustre,  fusibility  and  tests  for 
elements  are  the  classifying  tests,  and  the  Weisbach-(Frazer-Brown)  type,  in  which 
the  purpose  was  "to  help  the  determination  of  minerals  by  their  physical  char- 
acteristics" (preface  Weisbach's  Tabellen,  first  edition,  1866),  and  in  which  lustre, 
streak,  color,  sectility  and  hardness  are  the  classifying  tests. 

580 


TABLES  FOR  RAPID   DETERMINATION.  581 

In  discussing  this  addition  of  microscopic  tests  to  the  ordinary  mineral  schemes 
the  writer  said,*  "schemes  by  which  a  student  with  a  few  months'  experience  'deter- 
mines' the  identity  of  a  larger  or  smaller  series  of  the  more  common  or  important 
minerals  rarely  include  the  exact  easily  applied  distinctions  obtainable  with  the 
polarizing  microscope,  although  this  instrument  is  now  in  every  mineralogical 
laboratory  and  in  most  well  equipped  chemical  laboratories. 

"  If  the  polarizing  microscope  is  to  be  used  in  such  work  the  tests  must  be  quickly 
obtainable  and  accurate.  The  thin  sections  of  the  petrographer  will  not  therefore 
be  available,  nor  in  general  can  those  optical  characters  be  made  prominent  which 
are  only  obtainable  for  some  particular  direction  of  transmission  of  light.  In  my 
opinion  also,  for  this  particular  kind  of  scheme,  the  optical  characters  should  be 
made  subordinate  to  the  very  thoroughly  worked  out  so-called  'blowpipe  tests'  and 
'physical  tests.' " 

The  Tests  Leading  to  the  Key. 

In  the  tables  which  follow,  the  minerals  are  divided  first  into 
minerals  of  metallic  lustre  and  minerals  of  non-metallic  lustre 
(see  p.  210). 

The  minerals  of  metallic  lustre  are  sub-divided  into  twenty-four 
groups  by  the  tests  (or  characters) 

1.  Color,  see  p.  211. 

2.  Streak,  see  p.  212. 

3.  Heating  on  charcoal,  see  p.  169. 

The  minerals  of  non-metallic  lustre  are  divided  into  thirty-five 
groups  by  five  tests. 

'  i.  "Taste"  or  Solubility  in  Water. — See  p.  180.  The  test  is 
valuable  because  the  existence  of  a  "taste"  is  unmistakable, 
but  the  recognition  of  the  taste  is  not  easy. 

2.  Solubility  in  Dilute  Hydrochloric  Acid. — See  p.  180.     This 
test  fails  only  from  carelessness. 

3.  Treatment  on  Charcoal  with  Soda. — This  is  Test  II  of  page 
197. 

4.  Treatment  in  Platinum  Forceps. — This  is  the  "fusion  test." 
of  pp.  164  and  165.     The  scheme  and  the  safety  of  the  forceps 
both  require  that  the  absence  of  volatile  or  easily  fusible  elements 
should  first  be  proved  on  charcoal. 

5.  Flame  Coloration. — See  p.  165. 

*  Scheme  for  Utilizing  the  Polarizing  Microscope  in  the  Determination  of  Minerals 
of  Non-Metallic  Lustre,  by  A.  J.  Moses. 


582  DETERMINATIVE  MINERALOGY. 


The  Minor  Tests  of  the  Groups  1-24  and  2$A  to 

The  species  are  in  order  of  hardness  and  characters  of  deter- 
minative value  are  in  parallel  columns. 

Following  each  species  is  the  number  of  the  page  on  which  it 
is  described.  The  determination  must  always  be  confirmed  by  ref- 
erence to  this  description  and,  when  possible,  by  comparison  with 
known  specimens. 

The  Tests*  of  the  Alternative  Groups  256  to  296. 

The  tests  recorded  assume  the  use  of  crushed  fragments  but 
in  the  text  descriptions  of  the  species,  especially  in  the  silicates, 
special  optical  distinctions  are  given  for  thin  sections,  cleavages, 
etc. 

Crushing  and  Mounting  is  described  on  p.  126.  The  thickness 
of  the  resultant  grains  is  near  the  0.03  to  0.04  mm.  of  well  made 
thin  sections. 

The  Classifying  Tests  are  : 

i  .  The  relative  indices  of  refraction  of  the  grains  and  of  four  chosen 
mounting  liquids. 

2.  The  birefringence  of  the  grains  expressed  in  five  terms  deter- 
mined by  the  interference  colors. 

The  Relative  Indices  of  Refraction  are  determined  by  "The 
Becke  Test,"  p.  128,  and  "The  van  der  Kolk  Test,"  p.  129. 
The  scheme  considers  only  the  indices  of  refraction  corresponding 
to  the  two  positions  of  extinction  in  the  fragment. 

The  liquids  used  are: 

Index  at  15°  C. 
Xylol  .......................................    1,487 

Bromoform  ..................................    i,59O 

a  Monobrom-napthalin  .......................    1.655 

Methylene  Iodide  .....................  *  ......    i»74O 

The  Birefringence  is  approximately  determined  in  terms  of 
interference  colors  as  described  on  p.  137. 

Interference  Color.  Effect  of  Gypsum  Red.  Other  Tests. 

BLACK  Red  except  at  extinction  positions.  Unchanged  by  rotation. 

GRAY  OR  WHITE       Made  yellow  for  crossed  position, 

blue  or  purple  for  parallel  posi- 

tion. 
BRIGHT  A.  Made  white  or  gray  or  black  for 

crossed  position. 


TABLES  FOR   RAPID   DETERMINATION.  583 

BRIGHT  B.  Bright  colors  for  both  positions.  By  mica  plate  notably  dif- 

ferent tints  for  crossed 
and  parallel  positions. 

HIGH  ORDER.  Indefinite  colors  for  both  positions.  Not  noticeably  affected 

by  mica  plate  in  either 
position. 

Minor  Tests.    Upper  Nicol  Out. 

Shape.* — The  self-explanatory  terms  "laths,  "needles," 
"fibres,"  "triangles,"  "rhombs,"  "rectangles,"  and  "irregular" 
are  used.  The  term  "plates"  implies  flat  particles  lacking  straight 
edge  boundaries. 

Color  by  Transmitted  Light. — If  no  color  is  given  in  the  scheme, 
the  fragments  are  colorless. 
Pleochroism. — See  p.  153. 
Minor  Tests  with  Crossed  Nicols. 

Extinction  and  Extinction  Angles. — See  p.  138. 
The  method  of  designating  here  used  is: 
Ex.  1 1  when  the  angle  turned  is  zero. 
Ex.,  Sym.  when   the  angle  turned  is  one-half  the  angle 

between  two  crystalline  directions. 

Ex.,   Obi.  when   the  extinction  is  neither   "parallel"   nor 
"symmetrical,"  or  the  angle  may  be  stated,  e.  g.,  Ex.  27°. 
Elongation. — In  "laths,"  "needles,"  "fibres,  "etc.,  the  longer 
direction  or  "Elongation"  is  usually  a  crystallographic  direction. 
By  the  method  p.  134  its  "sign"  may  be  determined  as  EL,  (+) 
or  El.,  (-). 

Interference  Figure. — See  pp.  140  to  145. 
The  Optical  Sign  or  Character. — See  p.  146. 

Precautions.  / 

1.  The  specimen  should  first  be  carefully  studied  with  a  hand 
glass.     If  it  is  one  substance  so  far  as  this  shows  the  testing  may 
go  on.     If  not  fragments  of  the  different  substances  must  be 
obtained  and  separately  tested. 

2.  If  fine-grained  or  dull,  crushed  particles  should  be  examined 
with  the  microscope  as  to  homogeneity.     The  tests  will  be  un- 

*  Ciushing  tends  to  develop  the  cleavages,  and  in  a  liquid  the  fragments  tend  to 
lie  on  the  broadest  cleavage  surface,  thus  giving  considerable  constancy  in  shape  for 
fragments  of  each  mineral. 


584  DETERMINATIVE  MINERALOGY. 

reliable  if  the  material  is  impure,  unless  the  effect  of  the  impurity 
upon  the  test  is  known. 

3.  Lustres  and  colors  should  be  observed  on  fresh  fractures 
especially  in  minerals  of  metallic  lustre. 

4.  Classifying  tests  must  be  decided;   not  weak,  nor  indefinite. 
If  undecided,  the  species  on  both  sides  of  the  dividing  line,  must 
be  considered. 

5.  If  as  may  happen  the  tests  fit  no  species  in  the  scheme  or  do 
fit  some  species  the  description  of  which  is  radically  unlike  the 
specimen,  then  either  some  error  has  been  made  or  the  specimen 
belongs  to  a  species  not  included  in  the  scheme,  for  which  more 
elaborate  tables  will  be  needed. 

CONVENTIONS  AND  ABBREVIATIONS. 

The  species  in  each  group  are  printed  in  heavy  type  or  ordinary 
type,  according  to  their  importance.  The  formula  following  is 
expected  to  \uggest  confirmatory  blow-pipe  tests.  The  page 
reference  to  the  complete  description  of  the  species  is  also  given. 
H.,  is  hardness.  Sp.  gr.,  specific  gravity. 

Systems  of  Crystallization  are  indicated  by  the  letters:  I  (iso- 
metric), T  (tetragonal),  O  (orthorhombic) ,  M  (monoclinic),  Tri 
(triclinic),  H  (hexagonal). 

Terms  in  Blowpipe  Tests.  Soda  for  sodic  carbonate,  S.  Ph. 
for  salt  of  phosphorus,  O.  F.  and  R.  F.  for  oxidizing  and  reducing 
flame,  Co.  Sol.  for  cobalt  solution,  coal  for  charcoal,  Bi.Fl  for 
Bismuth  flux-,  Fl  for  flame,  subl.  for  sublimate.  The  numbers 
under  fusibility  are  the  v.  Kobell  scale,  p.  164.  The  "residue'* 
means  residue  after  fumes  have  ceased. 

Terms  in  Optical  Tests. 

Ex.,  ||;  Ex.,  Obi.;  Ex.,  22°;  Ex.,  Sym.,  denote  that  the  extinc- 
tion is  respectively  parallel,  oblique,  at  angle  of  22°,  and  sym- 
metrical. EL,  (+);  El.,  (-),  denote  that  the  elongation  is  (  +  ) 
or  (  — ).  I.  C.  is  for  interference  color,  <  for  less  than  and  > 
for  greater  than. 


TABLES  FOR   RAPID   DETERMINATION. 


585 


KEY. 

I.    MINERALS   OF  METALLIC   OR   SUBMETALLIC  LUSTRE. 


The  Color  is 

The  Streak  is 

HEATED  ON  CHARCOAL  YIELDS 

1< 

a  o 
a>"3 
"0 
< 

White  Coating 
But  no  Garlic 
Odor. 

iASi 

&5s 

gg? 

gll 

•s!*l 

8§fo 

bO-3'iS  o 

Us? 

a^"3 

Is*! 
fii° 

H 

Not  Previ- 
ously In- 
cluded. 

A.  Black  or  Nearly 

1.  Black 

I 

2 

3 

4 

5 

6 

2.  Not  Black 

7 

8 

9 

10 

B.  Silver-White,  Tin 
White  or  Gray 

1.  Black 

11 

12 

13 

14 

2.  Not  Black 

15 

16 

17 

18 

19 

20 

C.  Yellow,  Copper, 
Red,  Bronze,  or 
Blue 

1.  Black 

21 

22 

2.  Not  Black 

23 

24 

II.    MINERALS  OF  NON-METALLIC   LUSTRE. 


A.  Minerals  with  De- 

Which Color  the  Flame. 

25 

cided  Taste 

Which  do  not  Color  the  Flame. 

26 

WITH  HYDROCHLORIC  ACID  : 

Effer- 

Forms 

Dissolves 

Is  In- 

vesces. 

Jelly. 

only. 

soluble. 

Arsenical  Odor. 

27 

28 

B.  Tasteless,  but  with 
Soda  on  Charcoal  in 
the  Reducing  Flame 
Viplds  • 

Fumes  and  a  Metallic 
Globule. 
Fumes  but  not  a  Me- 
tallic Globule 

29 
32 

33 

30 
34 

31 

35 

No  Fumes  but  Magnetic 
Residue. 

36 

37 

Fuses  Easily  to  a  White 
Glass  or  Enamel. 

38 

39 

40 

41 

Fuses  Easily  to  a  Col- 
orless Glass. 

42 

43 

44 

Fuses  Easily  to  Colored 
Glass  or  Enamel. 

45 

46 

47 

48 

C.  Neither  A  nor  B 
but  Heated  in  Pt. 

Fuses  with  More  Diffi- 
culty   than    Common 

49 

50 

51 

52 

Forceps  : 

Orthoclase. 

Is  Infusible  but  in  Pow- 

der Made  Deep  Blue 

53 

54 

55 

by  Cobalt  Solution. 

Is  Infusible,  not  Made 

Deep  Blue  by  Cobalt 

56 

57 

58 

59 

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/»«)•            A.9 

Crystal  System  :  Name,  Composition, 
Hardness,  and  Specific  Gravity. 

Taste. 

On  Charcoal. 

Closed  Tube. 

i.  FLAME  YELLOW. 
ABSORBED  BY 
"COLOR  SCREEN" 

H.  Soda  Nitre,  p.  427, 
NaNOs 
H.,  1.5  to  2    Sp.  gr,  2.2 
M.  Mirabilite,  p.  426, 
Na2SO4  +  ioH2O 
H.,  1.5  to  2    Sp.  gr.,  1.5 
I.  Halite,  p.  425,  NaCl 
H.,  2.5  Sp.  gr.,  2  to  2.6 
M.  Trona,  p.  427, 
NaC03NaHC03.2  H2O 
H.,  2.5  to  3    Sp.  gr.,  2.1 

Cooling 
Bitter 
Salty 
Alkaline 

F.  =i.    Deflagrates 

F.  =1.5     and     will 
stain  silver 

F.=i.5 
F.=i 

With    KHS04 
brown  vapor 

Water 
A  little  water 
Water 

2.  FLAME  VIOLET 
THROUGH  COLOR 
SCREEN 

O.  Carnallite,  p.  420, 
KCl.MgC1.6  H20 
H.,  i              Sp.  gr.,  1.6 
O.  Nitre,  p.  420,  KNOa 
H.,  2              Sp.  gr.,  2.1 
I.  Kalinite,  p.  420, 
KAl(SO4)2  +  i2  H2O 
H.,  2.5           Sp.  gr.,  1.7 
M.  Kainite,  p.  420, 
MgS04KCl+3H20 
H.,  2.5  to  3 
Sp.  gr.,  2  to  2.2 

Salty    and 
bitter 

Salty    and 
cooling 
Astringent 

Salty    and 
bitter 

F.  =i   to   1.5.     Ig- 
nited with  Co.  sol. 
pink 
F.  =i.    Deflagrates 

F.  =  i.      Swells, 
froths,   will  stain 
silver 
F.  =  i  and  will  stain 
silver 

Much  water 

With    KHSO4 
brown  vapor 
Much    water, 
acid     at    high 
heat 
Water 

3.  FLAME 
GREEN 

M.  Borax,  p.  456, 
Na2B4O7+io  H2O 
H.,  2  to  2.5    Sp.gr.,  1.7 
Tri.  Sassolite,  p.  456, 
HsBOs 
H.,  i               Sp.  gr.,  1.4 
Tri.  Chalcanthite,   p. 
370,  CuSO4S  H2O 
H.,  2.5           Sp.  gr.,  2.2 

Sweetish 
alkaline 

Acid 

Metallic, 
nauseous 

F.  =i  to  1.5.  Swells 
and     gives     clear 
glass 
F.=2.      With    in- 
tumescence  to 
clear  glass 
F.  =  3.      Reduces 
with  effervescence 
to  copper  button 

Puffs  up.    Gives 
much  water 

Water  and  a 
little  ammonia 

Swells,   whitens. 
Yields  water 

25.     B.          (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Recrystallization  in  a  Drop  of 
Water. 

<  Xylol 
=  Xylol 

Black 
Gray  or  White 
Aggregate 

Gray  or  White 
to  Bright  A. 
Bright  A. 

Bright  A. 
Bright  A. 

Isotropic  3,  4,  6-sided  polygons 
Doub.     refr.    6-sided     polygons. 
Ex.,  [|   Bright    I.C.      Ex.  Obi. 
low  I.  C. 
Six-sided  plates   low  I.  C.,  and 
threads  bright  I.  C. 
Isotropic  rectangles,  doub.  refr. 
plates,  Ex.  Obi.  and  needles 
Isotropic  and  doub.  refr.  squares 
and  rectangles 
Laths.     Ex.,  |l. 

Kalinite 
Borax 

Sassolite 
Kainite 
Carnallite 

Thenardite 

Black 
Black 
Low 

Isotropic  squares  and  aggregates 
Isotropic  squares  and  "hoppers" 
Rectang.    laths    and    branching. 
Ex,  ||. 

Sylvite 
Halite 
Aphthitalite 

>  Xylol 

Gray  or  White 
Gray  or  White 
Bright  A. 
High  Order 

High  Order 

Spherulitic  aggregates 
Laths.     Ex.,  ||. 
Blue  crystals.     Ex.  Obi. 
Laths   Ex.,   ||   or    polygons     Ex. 
Sym.     Aggregates 
Rhombs.     Ex.  Sym.     High  I.  C. 

Trona 
Mirabilite 
Chalcanthite 
Nitre 

Soda  Nitre 

594 

26.   A. 


Crystal  System:  Name,  Composi- 
tion, Hardness  and  Specific  Gravity. 

Taste. 

On  Charcoal. 

•    Closed  Tube. 

I.  Sal  Ammoniac,  430,  NH4C1 

Saline 

White  fumes 

White  subl. 

H.,  1.5  to  2 

Sp.  gr.,  1.52 

M.  Alunogen, 

p.  4iS, 

Astringent 

Fuses,   becomes 

Much  water  a 

Al2(S04)3i8  H20 

infus.    Deep  blue 

S02 

H.,  1.5  to  2     Sp.  gr.,  1.6  to  1.8 

with  Co.  sol. 

M.  Melanterite,  p.  270, 

Astringent 

Darkens     becomes 

Like  alunogennd 

FeSO47H2O 

magnetic 

H.,   2 

Sp.  gr.,  1.9 

O.  Epsomite, 

P-  453, 

Bitter 

F. 

=  i    becomes 

Much  acid  water 

MgS047H20 

infus.     Pink  with 

H.,  2  to  2.  5 

Sp.  gr.,  1.7 

Co.  sol. 

O.  Goslarite,  p.  299, 

Astringent 

White  subl.  bright 

Water 

ZnS04.     7H20 

green  with  Co.  sol. 

H.,  2  to  2.5 

Sp.  gr.,  2.0 

M.  Copiapite, 

p.  270, 

Metallic, 

F. 

=4.5105  become 

Much  acid  water 

Fe3(OH)2(S04)6i8H20 

nauseous 

magnetic 

H.,2.5 

Sp.  gr.,  3.1 

H.  Coquimbite,  p.  270, 

Astringent 

Fuses   becomes 

Like  alunogen 

Fe2(S04)s9H20 

magnetic 

H.,  2  to  2.5 

Sp.  gr.,  2.1 

M.  Kieserite, 

p.  453, 

Fuses 

Much  water 

MgSO4.H2O 

H.,  3  to  3-5 

Sp.  gr.,  2.5 

26.    B. 

(CRUSHED   FRAGMENTS.) 

Index  of 
Refraction. 

Interference  Color. 

Recrystallization  in  a  Drop  of 
Water. 

Name. 

Gray  or  White 

Aggregate 

Laths.    Ex., 

||.    Spear  points 

Epsomite 

Ex.  Sym. 

Like  epsomite 

Kieserite 

Gray  or  White 

Branching  aggregates. 

Melanterite 

<  Xylol 

Rhombic  ends 

Gray  or  White 

Feathery.     Ex.,  ||. 

Alunogen 

Aggregate 

Like  epsomite 

Goslarite 

Black 

Aggregates  Ibranching  at  60° 

Sal  Ammoniac 

and  90°.     Isotropic 

>  Xylol 

Bright  B. 

No  recrystallization 

Copiapite 

Bright  A. 

Precipitate  on  heating 

Coquimbite 

27.   A. 

Crystal  System  : 
Name,  Composition, 
Hardness  and  Specific  Gravity. 

Fusibility 
(on  Coal). 

Closed 
Tube. 

Other  Tests. 

Usual  Color. 

M.  Annabergite,  p.  294, 

4 

Water 

See  p.  191  forNi 

Pale  green 

Ni3(AsO4)2+8H2O 

Pale   green 

H.,  1.5  to  2.  5 

streak 

M.  Erythrite, 

p.  292, 

2 

5 

Water 

Borax  deep  blue. 

Crimson  to  pink 

C03(As04)2.8H20 

0.  F.  and  R.  F. 

H.,  1.5  to  2.5 

Sp.  gr.,  2.9 

Streak  pink 

O.  Olivenite,  Cu2(OH)AsO4 

2  tO 

2-5 

Water 

Emerald    green 

Olive    green    to 

H.,  3 

Sp.  gr.,  4.4 

Fl. 

blackish 

H.  Mimetite, 

p.  323, 

I 

5 

White 

Greenish  yellow 

Yellow  brown 

Pb5Cl(AsO4)s 

subl. 

subl.   with   Bi 

H.,3-5 

Sp.  gr.,  7 

Fl. 

595 


27.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  Methylene 
Iodide 

Aggregate 
Bright  B. 

Greenish  hairs  or  aggregate 
Laths.      Pleochroic    pink    to 
red.     Ex.  about  32° 

Annabergite 
Erythrite 

>  Methylene 
Iodide 

Gray  or  White 
to  Bright  A. 
Bright  B. 

Irregular  .    Colorless,  greenish 
Irregular.     Green  to  yellow 

Mimetite 
Olivenite 

x»B.    A-» 

Crystal  System  : 
Name,    Composition, 
Hardness  and  Specific  Gravity. 

Fusibil- 
ity (on 
Coal). 

Closed  Tube. 

Other  Tests. 

Usual  Color. 

O.  Orpiment,  p.  330,  As2Ss 
H.,  1.5  to  2 
Sp.  gr.,  3.4  to  3-6 
M.  Realgar,  p.  329,  AsS 
H.,  1.5  to  2 
Sp.  gr.,  3.4  to  3.6 
H.  Proustite,  p.  388, 
Ag3AsS3 
H.,  2  to  2.5 
Sp.  gr.,  5.6  to  5.7 

I 
I 
I 

Boils.  Trans- 
parent yel- 
low subl. 
Boils.    Subl. 
black  hot, 
red  cold 
Fuses. 
Slight  red 
subl.  yel- 
low cold 

Sol.  HNOs  resi- 
due S.   Streak 
lemon  yellow 
Sol.    HN03. 
Streak  orange 
red 
Sol.    HNOs. 
Streak  scarlet 

Lemon  yellow 
Orange  red 
Ruby  red 

28.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

>  Methylene 
Iodide 

Bright    B.    or 
masked 
Bright    B.    or 
masked 
Masked 

Micaceous  plates  or  irregular 
Irregular.     Yellow  to  orange 
Irregular.     Brownish  orange 

Orpiment 
Realgar 
Proustite 

29.   A. 

Crystal  System  :   Name, 
Composition,  Hardness  and 
Specific  Gravity. 

Fusibil- 
ity (on 
Coal). 

Closed  Tube. 

Other  Tests. 

Usual  Color. 

O.  Cerussite,  p.  323, 
PbCOs 
H.,  3  to  3-5 
Sp.  gr.,  6.5  to  6.6 
T.  Phosgenite,  p.  324, 
(PbCl)2C03 
H.,  3                       Sp.  gr.,  6 
—  .  Bismutite,  p.  327, 
BiO.Bi(OH)2C03 
H.,  4.4                Sp.  gr.,  6.9 

1-5 
I. 

i-S 

Dark  yellow 
subl. 

Fusible 
sublimate 

Water 

Greenish  yellow 
with  Bi  flux 

Like  cerussite 

Chocolate    and 
red     with     Bi 
Flux 

Colorless  to 
white 

Colorless  to 
white 

White  to  yellow 

29.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

>  Methylene 
Iodide 

?  . 

Bright  A.  to  B. 
High  Order 
? 

Rectangular.     Ex.,     ||,     El., 
(+) 
Irregular  or  needles  with  Ex., 

Phosgenite 
Cerussite 

Bismutite 

596 


30.   A. 


Crystal  System:    Name, 
Composition,  Hardness  and 
Specific  Gravity. 

Fusibil- 
ity (on 
Coal.) 

Closed  Tube. 

Other  Tests. 

Usual  Color. 

M.   Kermesite,  p. 

335. 

I 

Blackens, 

Vol.  white  subl. 

Cherry  red 

Sb2S2O 

fuses,  dark 

coal.     Brown, 

H.,  i  to  1.5 

red  subl. 

red  streak 

Sp.  gr., 

4.5  to  4.6 

O.  Valentinite,  p 

335. 

1.5 

Fuses,  part- 

Vol.  white  subl. 

White 

Sb203 

1  y   s  u  b  - 

coal.    Fibrous 

H.,  2.5  to  3          Sp.  gr.,  5.6 

limes 

I.  Senarmontite, 

p.  335. 

1-5 

As  above 

Vol.  white  subl. 

White 

Sb203 

Octahedra 

H.,  2.5  to  3         Sp.  gr.,  5.2 

—  .  Bismite,  p.  327,  Bi2O3 

i.S(?) 

Water 

Erf  °n  coal 

White 

H.,                        Sp.  gr.,  4.3 

M.  Crocoite,  p.  346, 

1.5 

KHSO4 

Pb*     on     coal. 

Orange  red 

PbCr04 

dark    vio- 

S.  Ph.   green. 

H.,  2.5  to  3 

let   hot, 

Streak  orange 

Sp.  gr., 

5.9  to  6.1 

green  ish 

cold 

T.  Wulfenite,  p. 

350. 

2 

Darkens, 

Pb*   on    coal. 

Yellow  red  gray 

PbMo04 

decrepi- 

Mo p.  190 

H.,  3           Sp.  gr 

,  6.7  to  7 

tates 

H.  Vanadinite,  p 

338, 

1.5 

Pb*   on   coal. 

Red  brown  yel- 

PbbCUVOOs 

V.  p.  196 

low 

H.,  3        Sp.  gr.,  6.6  to  7.8 

O.  Descloizite,  p. 

339, 

3-5 

Water 

Pb*   on   coal. 

Black,  brown 

(PbOH)V04(Pb,Zn) 

V.  p.  196 

H.,  3.5      Sp.  gr., 

5.9  to  6.2 

H.  Pyromorphite 

p.  322, 

2 

On  coal  recrys- 

Green,   yellow 

Pb5Cl(P04)3 

tallizes,    Pb*. 

gray 

H.,  3.5  to  4 

P.  p.  204 

Sp.  gr., 

5-9  to  7.1 

—  .  Minium,  p.  321,  Pb3O4 

1.5 

Pb*  on  coal 

Red 

H.,  2.  to  3             Sp.  gr.,  4.6 

30.     B.            (CRUSHED  FRAGMENTS.) 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

Name. 

Bright  B. 

Needles.     Ex.,  || 

Valentinite 

Black 

Irregular 

Senarmontite 

Gray  or  White 

Irregular.    Colorless  to  green 

Pyromorphite 

to  Bright  A. 

Bright  B. 

Irregular   or   Laths.     Yellow 

Vanadinite 

>  Methylene 

to  orange 

Iodide 

Bright  B. 

Irregular.     Brown   to   green- 

Descloizite 

ish 

Bright  B. 

Irregular.    Pleochroic,  yellow 

Crocoite 

to  orange 

High  Order 

Irregular.     Yellow 

Wulfenite 

Masked 

Needles.     Ex.,  ||,  pleochroic, 

Kermesite 

ruby  red 

j> 

? 

Minium 

? 

? 

Bismite 

*  On  coal  with  Bi  Fl,  greenish  yellow  subl. 
t  On  coal  with  Bi  Fl,  chocolate  and  red. 

597 


31.   A. 


Crystal  System:    Name, 
Composition,  Hardness  and 
Specific  Gravity. 

Fusibil- 
ity (on 
Coal;. 

Closed  Tube  and  KHSO4. 

Usual  Color. 

Hot. 

Cold.       Sunlight. 

H.  lodyrite,  p.  392,  Agl 
H.,  1.5     Sp.  gr.,  5-6  to  5.7 
I.  Cerargyrite,  p.  391,  AgCl 
H.,  2  to  3     Sp.  gr.,  5  to  5.5 
I.  Bromyrite,  p.  392,  AgBr 
H.,  2  to  3     Sp.  gr.,  5.8  to  6 
I.  Embolite,  p.  392, 
Ag(Cl.Br) 
HM  2  to  3   Sp.  gr.,  5.3  to  5.8 
H.  Pyrargyrite,  p.  389, 
AgsSbSs 
H.,  2.5                 Sp.  gr.,  5.8 
M.  Linarite,  p.  322, 
[(PbCu)OH]2S04 
H.,  2.5       Sp.gr.,  5.3  to  5.4 
O.  Anglesite,  p.  321,  PbSO4 
H.,  3          Sp.  gr.,  6.1  to  6.4 
T.  Cassiterite,  p.  307,  SnO2 
H.,  6  to  7  Sp.  gr.,  6.8  to  7.1 

I 
I 
I 
I 

I 
1-5 

2-5 

7 

Deep  red 
Yellow 
Dark  red 
Dark  red 

Yellow    Yellow 
White     Violet 
Yellow    Green 
Yellow    Green 

Lemon  yellow 

Pearl     gray     to 
colorless 
Green  or  yellow 

Green  or  yellow 

Dark   red    to 
black 

Azure  blue 

Colorless   or 
white 

Brown  to  black 

Closed  Tube. 

On  Charcoal. 

Fuses.  Subl. 
black  hot, 
red  cold 
Whitens 
yields 
water 
Decrepi- 
tates 

White  and  later 
pink.    In  R.F. 
disappears 
With    Bi.Fl 
yellow     subl. 
and  green  Fl 
With    Bi.  Fl 
yellow  subl. 
With  soda  white 
subl.    bluish 
green  with  Co. 
sol. 

31.   B. 

(CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

>  Methylene 
Iodide 

Black 
Black 
Black 
Black 
Gray  or  White 
to  Bright  A. 
Bright  B. 
High 

Masked 

Irregular 
Irregular.     Greenish 
Irregular 
Irregular.     Yellowish 
Irregular 

Laths.     Ex.,  |[.     Blue 
Irregular.     Colorless  to  pleo- 
chroic  yellow 
Irregular.     Dark  red 

Cerargyrite 
Embolite 
Bromyrite 
lodyrite 
Anglesite 

Linarite 
Cassiterite 

Pyrargyrite 

32.   A. 

Crystal  System  : 
Name,  Composition, 
Hardness  and  Specific  Gravity. 

Fusibil- 
ity. 

Closed 
Tube. 

The  Sublimate  on 
Charcoal. 

Usual  Color. 

—  .  Hydrozincite,  p.  30, 
Zn3CO3(OH)4 
H.,  2.5     Sp.  gr.,  3.6  to  3.8 
H.  Greenockite,  p.  303, 
CdS 
H.,  3  to  3.  5  Sp.  gr.,  4.9  to  5 
I.  Sphalerite,  p.  298,  ZnS 
H.,  3.5  to  4 
Sp.  gr.,  3.9  to  4.1 
H.  Smithsonite,  p.  300, 
ZnCOs 
H.,  5          Sp.  gr.,  4.3  to  4.5 

7 
7 
7 
7 

Yellow    hot 
yields 
water 
Carmine 
hot,  yellow 
cold 

Yellow  hot, 
if  pure 

White  non  vol. 
Bright   green 
with  Co.  sol. 
Brown.      Often 
iris  tarnish 

Like   hydro- 
zincite 

Like   hydro- 
zincite 

Chalk  white 
Bright  yellow 
Brown  to  yellow 

Brown  to  nearly 
white 

598 

32.     B.              (CRUSHED    FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  a  Monobrom- 
Napthalin 

Black  or  Bright 
A. 

Irregular  or  Laths  with  Ex., 
||.     El.  <+) 

Hydrozincite 

>  a.  Monobrom- 
Napthalin 

Black 

p 
High  Order 

Triangles  and  irregular.    Yel- 
low.    Cleav.  at  60°,  90° 
Yellow 
Rhombs  with  Ex.,  Sym.  or  Ir- 
regular 

Sphalerite 

Greenockite 
Smithsonite 

33.   A. 

Crystal  System:   Name, 
Composition,  Hardness  and 
Specific  Gravity. 

Fusi- 
bility. 

Closed  lube. 

The  Sublimate 
on  Charcoal. 

Usual  Color. 

O.  Calamine,  p.  301, 
(ZnOH)2SiO3 
H.,  5         Sp.  gr.,  3.4  to  3.5 
H.  Willemite,  301,  Zn2SiO4 
H.,  5.5      Sp.  gr.,  3.9  to  4.2 

6 
5-5 

Water 

White  non  vol. 
bright   green 
with  Co.  sol. 
Like  calamine 

White,  yellow 

Yellow,     brown, 
greenish 

34.   A. 

O.  Molybdite,  350,    MoO3 
H.,  i  to  2            Sp.  gr.,  4.5 
H.  Zincite,  p.  299,  ZnO 
H.,  4.5     Sp.  gr.,  5.4  to  5.7 

2(?) 
7 

Blackens 

White.        Deep 
blue  by  R.  F. 
Like  calamine 

Yellow 

Deep    to    brick 
red 

35.   A. 

T.  Calomel,  p.  377,  Hg2Cl2 
H.,  i  to  2           Sp.  gr.,  6.5 
O.  Sulphur,  p.  463,  S 

Vol. 

i 

Mirror  with 
soda 
Fusible  subl. 

White  volatile 
None,    but 

White,   colorless 
Yellow  brown 

T.  Calomel,  p.  377,  Hg2Cl2 

Vol. 

Mirror  with 

White  volatile 

White,   colorless 

H.,  i  to  2            Sp.  gr.,  6.5 

soda 

O.  Sulphur,  p.  463,  S 

i 

Fusible  subl. 

None,    but 

Yellow  brown 

H.,  1.5  to  2.5 

brown   hot 

strong    SO2 

Sp.  gr.,  2.0  to  2.1 

yellow  cold 

fumes 

H.  Cinnabar,  p.  376,    HgS 

Vol. 

Mirror  with 

None 

Vermilion,   scar- 

H., 2  to  2.5         Sp.  gr.,  8.1 

soda 

let,  red 

I.  Gahnite,  p.  302,  ZnAlOi 

Unchanged 

Weak   but   like 

Green,  brown, 

H.,  7.5  to  8     Sp.  gr.,  4  to  4 

7 

calamine 

black 

33.     B.             (CRUSHED   FRAGMENTS.) 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

Name. 

<  a  Monobrom- 

Bright  B. 

Laths.     Ex.,  ||.     El.  (+) 

Calamine 

Napthalin 

>  «  Monobrom- 

Bright  A.  to  B. 

Irregular.     Colorless   to 

Willemite 

Napthalin 

brown 

34.    B. 


>  Methylene 
Iodide 


Masked 


Laths   or   irregular.      Yellow 

to  orange 
Minute  needles,  Ex.,  I 


Zincite 

Molybdite 


35.    B. 


>  Methylene 
Iodide 

Masked 
High  Order 
Black 
Hi.eh  Order 

Irregular.     Brilliant  red 
Rhombs  and  rectangles 

Irregular 

Cinnabar 
Calomel 
Gahnite 
Sulphur 

599 


36.   A. 


Crystal  System  : 
Name,  Composition, 
Hardness  and  Specific  Gravity. 

Fusibil- 
ity. 

Closed  Tube. 

Streak. 

Usual  Color. 

H.  Siderite,  p.  275,  FeCO3 
H.,  3-5  to  4 

Sp.  gr.,  3.8  to  3.9 

5 

Black  mag- 
netic 

Nearly  white  if 
pure 

Light  to  dark 
brown.  Cleav- 
able  or  granular 

37.   A. 


M.  Vivianite,  p. 

472, 

2  to  2.  5 

Water. 

Blue 

Bluish   green 

Fe3(P04)2+8H20 

(Turns 

earthy     to 

H.,  1.5  to  2 

brown) 

blackish     blue 

Sp.  gr., 

2.6  to  2.7 

crystals 

—  .  Garnierite,  p 

.  294, 

7 

Water   de- 

Pale green 

Deep    green    to 

H2(Ni,Mg)Si04+H20 

crepitates 

pale  green 

H.,  2  to  3  Sp.gr., 

2.3  to  2.  8 

—  .  Limonite,  p. 

274. 

5  to  5.  5 

Much  water. 

Yellowish  brown 

Yellowish  brown 

Fe203.Fe2(OH)6 

Reddens 

to  nearly  black. 

H.,  5  to  5.5  Sp.  gr.,  3.6  to  4 

i     Not  crystals 

O.  Goethite,  p.  273, 

5  to  5.5 

Water. 

Yellowish  brown 

Yellowish  brown 

FeO(OH) 

Reddens 

to  nearly  black. 

H.,  5  to  5.  5  Sp.gr.,  4  to  4.4 

Often  crystals 

—  .  Turgite,  p.  274, 

StoS-S 

Flies  to 

Brownish  red 

Red     to     black 

Fe406(OH)2 

pieces. 

crusts 

H.,  5.5  to  6 

Water 

Sp.  gr., 

4-3  to  4.7 

H.  Hematite,  p.  271,  Fe2O3 

7 

Brownish  red 

Dull  dark  red 

H.,  5.5  to  6.5 

Sp.  gr., 

4-9  to  5.3 

36.   B. 

(CRUSHED   FRAGMENTS.) 

Index  of 

Interference 

Name. 

Refraction. 

Color. 

Other  Notable  Characters. 

>  Methylene 
Iodide 

High  Order 

Rhombs.     Ex.  Sym. 
Index    |j    short    diag.  closely 

Siderite 

that  of  methvlene  iodide 

37.    B. 


<  Methylene 
Iodide 

Gray  or  White. 
Aggregate 
Bright  B. 

Irregular.     Greenish 

Laths.     Ex.,  ||.     El.,  (+)  or 
Ex,  30°  El.,  (  -).    Pleochroic 
blues  or  colorless 

Garnierite 

Vivianite 

>  Methylene 
Iodide 

Bright  B. 
High  Order 

? 
Masked 

Yellow  fibres,  Ex.,  Obi.,  and 
irregular,  opaque 
Laths  Ex.  ,  1  1  .     Pleochroic  yel- 
low 
Irregular.     Opaque 
Dark  red  or  opaque 

Limonite 
Goethite 

Turgite 
Hematite 

600 


38.    A. 


Crystal  System  : 
Name,  Composition, 
Hardness  and  Specific  Gravity. 

Fusibil- 
ity. 

Flame 
Coloration. 

Other  Tests. 

Usual  Appearance. 

M.  Gaylussite,  p.  427, 

i-5 

Yellow 

Closed   tube 

White  crystals 

CaNa2(C03)25H20 

water 

H.,  2  to  3             Sp.  gr.,  1.9 

O.  Witherite,  p.  433, 

2 

Yellowish 

Solution  gives 

White  columnar 

BaCOa 

green 

ppt  with  H2SO4 

and  pseudo- 

H.,  3  to  4           Sp.  gr.,  4.3 

hexagonal 

H.  Cancrinite,  p.  570, 

2 

Yellow 

Jelly  on  heating 

Yellow  or  white 

R(Na2C03)(Si04) 

solution 

massive 

H.,  5  to  6            Sp.  gr.,  2.4 

39.   A. 

O.  Thomsonite,  p.  534, 

2 

I  n  t  u  mesces. 

White    radiated 

(Na2Ca)Al2Si208+sH20 

Much  water 

or  green  spher- 

H., 5  to  5.5        Sp.  gr.,  2.4 

ical 

M.  Pectolite,  p.  535, 

2 

Yellow 

Water  in  closed 

White  radiating 

HNa2Ca(SiO3)3 

tube 

fibres 

H.,  5                    Sp.  gr.,  2.7 

M.  Wollastonite, 

P-  507. 

4 

Red 

Often  effervesce 

White   semi- 

CaSiOs 

from  calcite 

fibrous  or  gray 

H.,  4.5  to  5        Sp.  gr.,  2.8 

crystals 

I.  Lazurite,  p.  576, 

3-5 

Yellow 

Blue   in   fine 

Deep  blue,  usu- 

Na4(NaS3Al)    Al2(SiO4)3 

powder.   Odor 

ally  spangled 

H.,  5  to  5.5        Sp.  gr.,  2.4 

H2S  with  acid 

with  pyrite 

H.  Chabazite,  p. 

532, 

3 

I  ntu  mesces 

Nearly   cubic; 

(CaNa2)Al(Si04)36H20 

Striated. 

H.,  4.5      Sp.  gr., 

2.O  tO  2.1 

White  and  pink 

T.  Apophyllite,  p 

534. 

2 

Pale    violet 

One  easy  cleav- 

Colorless    cubic 

Hi4K2Ca8(SiO3)i69H2O 

(Color 

age.  Exfoliates 

or   pointed 

H.,  4.5  to  5 

Screen) 

during  fusion 

crystals  with 

Sp.  gr., 

2.3  to  2.4 

opalescence   in 

direction  c 

38.   B 

(CRUSHED   FRAGMENTS.) 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

Name. 

<  Bromoform 

Bright  A. 

Plates  or  Laths.     Ex.,  || 

Cancrinite 

>  Bromoform 

High  Order 

Plates  or  Laths  with  Ex.,  ||. 

Witherite 

El.,  (-). 

39.    B. 


<  Bromoform 

Black 
Gray  or  White 

Gray  or  White 
Gray  or  White 
to  Bright  A. 

Blue  included  particles 
Rectangular.     Ex.,   |j  or  iso- 
tropic  with  uniaxial  I.  F. 

Rhombs.     Ex.  Sym. 
Laths.     Ex.,  H 

Lazurite 
Apophyllite 

Chabazite 

Thomsonite 

>  Bromoform 

Gray  or  White 
Bright  A. 

Laths    or    Needles.     Ex.     ||. 
El.,  (+) 
Needles.     Ex.,  ||.     El.,  (+) 

Wollastonite 

Pectolite 

601 


40.   A. 


Crystal  System:  Name, 
Composition,  Hardness  and 
Specific  Gravity. 

Fusi- 
bility. 

Flame 
Coloration. 

Other  Tests. 

Usual  Appearance. 

M.  Gypsum,  p.  443. 

3  to  3.  5 

Yellowish 

Cleaves   to   a 

Colorless   "sele- 

CaS04+2H20 

red 

rhombic  plate 

nite."      White 

H.f  i.  5  to  2        Sp.  gr.,  2.3 

of  66°.     Solu- 

or tinted  scaly 

tion  recrystal- 

or      fibrous 

lizes 

masses 

M.  Cryolite,  p.  412, 

1-5 

Yellow 

Blue   if   ignited 

Translucent    re- 

AlNa3F2 

with  Co.  sol. 

sembling 

H.,  2.5         Sp.  gr.,  2.9  to  3 

watery  snow 

O.  Anhydrite,  p.  442, 

3  to  3-5 

Yellowish 

Cleaves    three 

Blue  and  white. 

CaS04 

red 

directions   at 

Cleavable   and 

H.,  3  to  3-5  Sp.gr.,  2.9  to  3 

90° 

fine-grained 

M.  Heulandite,  p.  534. 

3 

Swells  withheat. 

White     or     red 

H4CaAl2(Si03)6+3H20 

Lozenge  shaped 

crystals 

H.,  3.5  to  4        Sp.  gr.,  2.2 

pearly  face 

M.  Stilbite,  p.  533, 

3 

Swells   greatly 

Sheaf  -1  i  ke 

H4R2Al2(SiO3)6  +4H2O 

during  fusion. 

groups  or  many 

H.,  3-5  to  4 

Symmetrical 

small  brown  or 

Sp.  gr.,  2.1  to  2.2 

pearly  face 

white   crystals 

I.  Fluorite,  p.  441,  CaF2 

3 

Red  to 

Phosphorescent. 

Glassy  cubes  of 

H.,  4           Sp.  gr.,  3  to  3.3 

orange 

Cleavages     at 

purple    yellow 

70°  3  1' 

and  green 

M.  Harmotome,  p.  534, 

3 

Whitens  before 

White  or  color- 

(BaK2)Al2Si5Oi4.5H2O 

fusing 

less   crossed 

H.,  4-5                 Sp.  gr.,  2.5 

twins 

T.  Wernerite,  group  p.5i5, 

3 

Yellow 

Bubbles  in  fused 

Gray  and  green- 

(Silicates  of  NaCaAl) 

material.  Clea- 

ishoctagonalor 

H.,  5  to  6           Sp.  gr.,  2.7 

vages  at  90° 

square  prisms 

O.  Prehnite,  p.  535, 

2-5 

Intumesces. 

Green     rounded 

H2Ca2Al2(Si04)3 

Bubbles   in 

crusts  or  sheaf- 

H.,  6  to  6.5  Sp.gr.,  2.  8  to  2.9 

fused  material 

like  groups 

I.  Boracite,  p.  458, 

3 

Yellowish 

Violet  if  ignited 

Minute   glassy 

Mg7Cl2Bi6O3o 

green 

with  Co.  sol. 

crystals 

H.,  7           Sp.  gr.,  2.9  to  3 

40.     B*             (CRUSHED    FRAGMENTS.) 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

Name. 

Black 

Polygons  3,  4,   5  or  6-sided, 

Fluorite 

<Xylol   ' 

Gray  or  White 

angles  60°  and  120° 
Roughly  rectangular 

Cryolite 

Ex.  Obi.  large  angle 

Gray  or  White 

Laths.     Ex.,  ||.     El.,  (—  )  or 

Heulandite 

Ex.,  25°  to  30° 

Gray  or  White 

Rhombic  Laths  and   Fibers. 

Gypsum 

to  Bright  A. 

Ex.  Obi. 

>  Xylol 

Gray  or  White 

Laths.     Ex.,  j|.     El.,  (-) 

Stilbite 

<  Bromoform 

to  Bright  A. 

Bright  B. 

Rectangles.     Ex.,    |[.      Diag- 

Anhydrite 

onal  striations 

Bright    B.or 

Laths.      Ex.,    ||.      El.,    (-). 

Wernerite 

High  Order 

Inclusions 

Bright  A. 

Laths.      Ex.,     ||.      El.,     (-) 

Prehnite 

>  Bromoform 

Bright  A. 

and  irregular 
Irregular 

Boracite 

Bright  B. 

See  above 

Anhydrite 

602 


41.   A. 


Crystal  System  : 

Fusibil- 

Flame 

Name,  Composition, 

ity. 

Coloration. 

Other  Tests. 

Usual  Appearance. 

Hardness  and  Specific  Gravity. 

M.  Lepidolite,  p.  429, 

2 

Crimson 

Acid    water    in 

Lilac     or     pink 

(KLi)3Al(SiO3)3 

closed  tube. 

scaly  masses  or 

H.,  2.5      Sp.gr.,  2.8  to  3.2 

Easy   cleavage 

gray    plates 

O.  Barite,  p.  432,  BaSO4 

4 

Yellowish 

Cleaves   to 

White  and  and 

H.,  2.5  to  3-5 

green 

rhombic  plates 

tinted       crys- 

Sp. gr.,  4.3  to  4.6 

of  78.    Heavy 

tals  and  masses 

O.  Celestite,  p.  435,  SrSO4 

3-5to4 

Crimson 

Cleaves     to 

Pale  blue  white 

H.,  3  to  3.5           Sp.'gr.,  4 

rhombic  plates 

crystals       and 

of  76°.   Heavy 

fibrous 

M.  Amphibole,  (tremolite), 

4 

Cleavage      and 

White   fibrous 

p.  508,     CaMg3(SiO3)4 

prism  124°  30' 

radiating   or 

H.,5to6  Sp.gr.,  2.9  to  3.4 

prisms 

M.  Pyroxene,    (diopside). 

4 

Cleavage      and 

White   or   green 

p.  506,       CaMg(SiOs)2 

prism  87°  51 

inclined    8- 

H.,  5  to  6  Sp.gr.,  3.  2  to  3.6 

sided     prisms 

O.  Zoisite,  p.  528, 

3  to  3 

5 

Swells  and  fuses 

Gray  brown  col- 

Ca2(AlOH)Al2(SiO4)3 

to   bubbly 

umnar.     One 

H.,  6  to  6.5         Sp.  gr.,  3.3 

glass 

easy    cleavage 

M.  Petalite,  p.  430, 

4 

Crimson 

Phosphorescent 

Colorless   or 

LiAl(Si205)2 

on  heating 

white   cleav- 

H.,  6  to  6.5         Sp.  gr.,  2.4 

able 

Tri.  Plagioclase,  p.  494, 

4  to  4 

5 

Yellow 

Cleavage    87° 

White,    gray, 

See  44-A. 

approx. 

red.      Striated 

Tri.  Amblygonite,  p.  428, 

2 

Crimson   to 

Momentary 

White    masses 

Li(AlF)PO4 

yellowish 

blue-green  Fl. 

with   one  easy 

II.,  6            Sp.  gr.,  3  to  3.1 

red 

with  H2SO4 

cleavage 

H.  Tourmaline,  p.  524, 

3-5 

Green  with 

Electric  by  heat 

Brown    prisms 

Ri8B2(Si06)4 

KHSO4 

or  friction 

often     trigonal 

H.,  6  to  6.5 

+CaF2 

and    hemimor- 

Sp.  gr.,  2.8  to  2.9 

phic 

M.  Spodumene,  p.  429, 

3-5 

Crimson 

Sprouts   during 

White,  green  and 

LiAl(Si03)2 

fusion.  Cleav- 

pink  crystals 

H.,  6.5  to  7 

age  at  87° 

often  lamellar 

Sp.  gr.,  3.1  to  3.2 

41.     B.              (CRUSHED    FRAGMENTS.) 

Index  of                       Interference 
Refraction.                        Color. 

Name. 

Other  Notable  Characters. 

Laths  and  Plates.     Twinning 

Plagioclase 

Gray  or  WThite 

<  Bromoform           to  Bright  A. 

See  p.  491  for  varieties 

Petalite 

Bright  A.  to  B 

Plates 

Amblygonite 

• 

Rectangular,  Ex.,  ||  ;  or  rhom- 

Barite 

bic,  Ex.  Sym.;  or  irregular 

>  Bromoform        G          rWhite 
t^gSStr.        to  Bright  A/ 

Like  barite 
Plates  and  Rhombs.     Biax. 
Laths    or    fibres.     Ex.    Obi. 

Celestite 

Lepidolite 
Amphibole 

El.    (+).      See    p.    502 

Irregular 

Tourmaline 

Gray  or  White 

Plates 

Zoisite 

>a-Monobrom-    ^  °\™Jite 

Laths.     Ex.,  2o°-25°  El.,  (  +) 

Spodumene 

,T     ,    ,    ,.              to  Bright  A. 
Naphthalm        Brjght  A   tQ  B 

Laths    and     Rhombs.        Ex. 

Pyroxene 

Obi.  see  p.  502 

603 


42.    A. 


Crystal  System:  Name, 
Composition,  Hardness  and 
Specific  Gravity. 

Fusibil- 
ity. 

Flame 
Coloration. 

Other  Tests. 

Usual  Appearance. 

H.  Nephelite,  p.  499. 

4 

Yellow 

Blue    with    Co. 

Gray  or  reddish, 

Na»Al8Si»Os4 

sol. 

greasy  massive. 

H.,  5  5  to  6 

Also     smal) 

Sp.  gr.,  3-2  to  3.6 

white  prisms  - 

O.  Natrolite,  p.  532, 

2-5 

Yellow 

Quiet  fusion 

White  needles 

Na2Al2Si3Oio 

nearly  .square 

H.,  5  to  5-5         Sp.  gr.,  2.2 

with  flat  pyra- 

midal ends 

I.  Analcite,  p.  531, 

3 

Yellow 

Becomes  opaque 

White  or  color- 

NaAl(SiO3)2.H2O 

before  fusion 

less  trapezohe- 

H.,  5  to  5-5 

dra 

Sp.  gr.,  2.2  to  2.3 

M.  Datolite,  p.  536, 

2  tO  2.  5 

Green 

Intumesces 

Bright    colorless 

Ca(BOH)Si04 

complex    crys- 

H., 5  to  5-5  Sp.  gr.,  2.9  to  3 

tals.    Porcelain 

masses 

I.  Sodalite,  p.  500 

3-5  to4 

Yellow 

Closed  tube 

Gray,  blue,  etc. 

Na.Al.Cl.Si 

whitens 

massive     and 

H.,  5.5  to  6        Sp   gr.,  2.2 

crystals 

43.    A, 


—  .  Ulexite,  p.  457, 
CaNaB5O9.8H2O 
H.,  i                   Sp.  gr.,  1.65 
M.  Colemanite,  p.  458, 
Ca2B6On.5H2O 
H.,  4  to  4.5 
Sp.  gr.,  2.2  to  2.3 
Tri.  Plagioclase,  p.  494, 
wNaAlSisOs  +mCaA!2 
Si208 
H.,  5  to  6.5 
Sp.  gr.,  2.5  to  2.8 

i  5 
1-5 

4  to  4.5 

Reddish 
yellow 

Green 
Yellow 

Solutions   de- 
posit   crystals 
of  sassolite 

Two  easy  cleav- 
ages (86°,  87°, 
etc.).      Varie- 
ties by  scheme 
P-  491 

White   fibres   in 
"  Cotton  balls" 

Colorless   com- 
plex crystals. 
White,    chalky 
or  porcelain 
WThite,  gray,  red- 
dish, cleavable, 
striated 

42.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

Equal 
Xylol 

Black   or   Gray 
or  White 
Black 
Gray  or  White 
to  Bright  A. 

Irregular  glassy 

Needles  and  Laths.     Ex.,  ||. 
El.  (+) 

Analcite 

Sodalite 
Natrolite 

>  Xylol 
<  Bromoform 

Gray  or  White 

Irregular  or  Laths  with  Ex., 
||.     El.  (-) 

Nephelite 

>  Bromoform 

Bright  B. 

Irregular 

Datolite 

43.    B. 


<  Bromoform 

Gray  or  White 

Gray  or  White 
or  Bright  A. 

Fine    needles.     Ex.,    ||. 
(-) 
Plates  and  Laths.     Ex. 
see  p.  

El. 
Obi. 

Ulexite 
Plagioclase 

Equal  or  > 
Bromoform 

Bright  A. 

Plates 

Colemanite 

44.     Certain 
work  out  here. 


varieties  of  Plagioclase,  Amphibole,  Pyroxene  and  Spodumene  may 
In  this  case  use  41.  A.  and  B. 

604 


45.    A. 


Crystal  System  : 
Name,  Composition, 
Hardness  and  Specific  Gravity. 

Fusi- 
bility. 

Flame 
Coloration. 

Other  Tests. 

Usual  Appearance. 

M.  Malachite,  p. 

37i. 

3 

Green,  blue 

Closed   tube, 

Bright    green 

Cu2(OH)2CO3 

with  HC1 

black   much 

fibrous     in- 

H.,  3.  5  to  4  Sp.gr.,  3.9  to  4 

water 

crusting  or  dull 

M.  Azurite,  p.  371, 

3 

Like   mala- 

Like malachite. 

Dark-blue  glassy 

Cu3(OH)2(C03)2 

chite 

Streak  blue 

crystals,  velvety 

H.,  3-5  to  4        Sp.  gr.,  3.8 

or  dull  crusts 

46.   A. 

T.  Mellilite,  p.  499, 

3 

Intumesces 

White  or  yellow- 

Complex Silicate 

ish    small 

H.,  5         Sp.  gr.,  2.9  to  3.1 

square  prisms 

M.  Allanite,  p.  529, 

2-5 

Swells,  becomes 

Black  "nail1'  or 

"Cerium  Epidote" 

magnetic 

plate  crystals 

H.,  5.  5  to  6  Sp.gr.,  3-5  to  4 

O.  Tephroite,  p.  285, 

3-5 

Amethyst  borax 

Ash  gray  to  red- 

Mn2SiO4 

bead 

dish  masses 

H.,  5.5  to  6        Sp.  gr.,  4.1 

45.   B. 

(CRUSHED   FRAGMENTS.) 

Index  of  Refraction. 

Interference  Color 

Other  Notable  Characters. 

>  Methylene 

Tr>HiHf» 

Masked 
Masked 

Irregular.      Blue 
Laths.     Ex.  Obi.    Arrowhead 

Azurite 
Malachite 

twins.     Green 

46.    B. 

<  a-Monobrom- 

Gray  or  White 

Plates 

Melilite 

Naphthalin 

Bright  B. 

Irregular.    Brown,  pleochroic 

Allanite 

>  Methylene 

High  Order 

Plates.     Pleochroic 

Tephroite 

Iodide 

47.   A. 

Crystal  System  . 
Name,  Composition, 
Hardness  and  Specific  Gravity. 

Fusibil- 
ity. 

Flame 
Coloration. 

Other  Tests. 

Usual 
Appearance. 

O.  Autunite,  p.  345, 

3 

Yellowish 

Borax  colorless 

Yellow      square 

Ca(U02)2(P04)2+8H20 

red 

O.    F.,    green 

plates       scales 

H.,  2  to  2.  5   Sp.gr,  3  to  3.  2 

R    F.     See  p. 

and  aggregates 

T95 

T    Torbernite,  p. 

345, 

3 

Azure    blue 

Borax  green  O 

Pearly   green 

Cu(UO2)2(PO4)2  +8H2O 

with   HC1 

F.  red  R.  F. 

plates 

H.,  2  to  2.5 

Sp.  gr., 

3.4  to  3.6 

t 

O.  Atacamite,  p. 

370, 

3  to  4 

Azure    blue 

White  and   red 

Emerald-green, 

Cu2(OH)3Cl 

sublimates 

aggregates  and 

H.,  3  to  3-5 

prisms 

Sp.  gr., 

3.7  to  3-8 

O.   Brochantite,  p.  370, 

3-5 

Green,  blue 

Fused  with  soda    Emerald-green 

CuSO4.3Cu(OH)2 

with  HC1 

stains  silver           needles      and 

H.,  3.5  to  4        Sp.  gr.,  3.9 

crusts 

I.  Cuprite,  p.  368,  Cu2O 

3 

Azure-blue 

Streak  brownish 

Dark-red 

H.,  3.5  to  4 

with  HC1 

red 

masses    and 

Sp.  gr., 

5.8  to  6.1 

crystals  or 

hair-like 

605 


47.     B.              (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  Bromoform 

Gray  or  White 

Plates.     Pale  yellow 

Autunite 

>  Bromoform 
<  a-Monobrom- 
Naphthalin 

Black 
Bright  A. 

Rectangles.     Uniax.     Green 
Laths.     Ex.,  ||.     EL,  (—  )  or 
Irregular 

Torbernite 
Prehnite 

>  Methylene 
Iodide 

Black 
Bright  A. 

Masked 

Irregular  or  Needles-     Red 
Laths.      Ex.,     ||,    El.,     (+). 
Green 
Plates    or    Laths.     Ex.,     ||. 
Green 

Cuprite 
Brochantite 

Atacamite 

48.   A. 


Crystal  System  : 
Name,  Composition,  Hardness 
and  Specific  Gravity, 

Fusibility. 

Flame 
Colora- 
tion. 

Other  Tests. 

Usual  Appearance. 

M.  Roscoelite,  p.  340, 

3 

S.  Ph.  0.  F  yel- 

Dark  green 

"Vanadium  Mica" 

low  R.  F.  green 

scales 

H.,  2  ?                     Sp.  gr.,  2.9 

—  .  Crocidolite,p.509,NaFeSi 

3-5 

Yellow 

After   fusion   is 

Blue  fibres 

H.,  4                        Sp.  gr.,  3.3 

magnetic 

M.  Titanite,  p.  525, 

4 

S.  Ph.  O.F.  then 

Brown  or  green 

CaSiTiOs 

R.    F.    violet 

"e  n  vel  o  pe" 

H.,  5  to  5-5    Sp.gr.,  3.4  to  3.5 

Cleavages  113° 

and     wedge 

shaped  crystals 

M.  Pyroxene,  p.  505, 

4 

Cleavage     and 

Green   to    black 

RSiOs.       Many  varieties 

prism     angles 

inclined  prisms 

H.,  5  to  6     Sp.  gr.,  3.2  to  3.6 

87°  5' 

Cross     section 

8-sided. 

M.  Amphibole,  p.  507, 

4 

Cleavage      and 

Green   to   black 

RSiOs.      Many  varieties 

prism  angles 

fibrous  or  pris- 

H.,  5  to  6     Sp.  gr.,  2.9  to  3.4 

124°  30' 

m  a  c  i  c   with 

rhombic  or  six- 

sided     section. 

O.  Hypersthene,  p.  505, 

5 

After  fusion   is 

Black   foliated 

(Mg.Fe)SiO3 

magnetic 

sometimes 

H.,  5  to  6      Sp.  gr.,  3.4  to  3.5 

pearly 

Tri.  Rhodonite,  p.  284, 

3  to  3.5 

Borax,     O.     F. 

Red    or    brown 

MnSiOs 

amethystine 

fine-grained  or 

H.,  6  to  6.5    Sp.gr.,  3.4103.7 

cleavable. 

M.  Epidote,  p.  528, 

3  to  4 

After  fusion  will 

Pistache    or 

Ca2(Al.Fe)2  (A1OH)  (SiO4)3 

gelatinize 

blackish   green 

H.,  6  to  7      Sp.  gr.,  3.2  t.  3.5 

Water  in  closed 

grains       or 

tube 

needles 

T.  Vesuvianite,  p.  511, 

3 

After  fusion  will 

Brown,  or  green 

Ca2Al3(Oh.F)  (Si04)2 

gelatinize. 

square    prisms 

H.,  6.5         Sp.  gr.,  3.3  to  3.4 

Water  in  closed 

or  columnar  or 

•tube 

compact 

Tri.  Axinite,  p.  570, 

2  to  3 

Green 

Intumesces 

Brown  or  violet. 

H2R4(BO)Al3(Si04)5 

with 

"Axe"  shaped 

H.,  6.5  to  7             Sp.  gr.,  3.3 

Bo.  Fl. 

I.  Garnet,  p.  509, 

3  to  4 

After  fusion  will 

Brown  or  red  12, 

R3R2(Si04)3 

gelatinize.  Often 

24  and  36  faced 

H.,  6.5  to  7.5 

nearly  spherical 

crystals 

Sp.  gr.,  3.1  to  4.3 

H.  Tourmaline,  p.  524, 

3  to  5 

Green 

After  fusion  will 

Black  opaque, 

R«Bi(SiOB)< 

with 

gelatinize.  Often 

brown,   and 

H.,  7  to  7.5      Sp.gr.,  3  to  3  2 

Bo.  Fl. 

roughly      tri- 

bright   colored 

angular 

prisms 

606 


48.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  a-Monobrom- 
Naphthalin 

Gray  or  White 
to  Bright  A. 
Bright  A.  to  B. 

Irregular.      Pleochroic   black 
to  smoky 
Laths.     Ex.,    10°  —  20°.     El. 
(+) 
Pleochroic    green    to    yellow 
Pleochroic  green  to  yellow 
Pleochroic  green  to  brown 

Tourmaline, 

(Dark  Varieties) 
Amphibole, 
see  p.  502 
Actinolite 
Pargasite 
Hornblende 

>  a-Monobrom- 
Naphthalin 
<  Methylene 
Iodide 

Gray  or  White 
Gray  or  White 
Bright  A. 
Bright  A.  to  B. 

Bright  B. 

Irregular 
Irregular 
Laths.    Ex.,  10°,  El.  (+) 
Laths  and  Rhombs.     Ex.,  30 
to  54°.     Rarely  pleochroic 

Pleochroic.     Brown.     Ex.,  o° 
to  10°.     El.  (+) 

Axinite 
Vesuvianite 
Rhodonite 
Pyroxene, 
see  p.  502 
Hedenbergite, 
Augite 
Amphibole, 
Basaltic  Horn- 
blende 

>  Methylene 
Iodide 

Black 
Bright  B. 
High  Order 

Abnormal  Apple 
Green 

Irregular.       Tinted     reddish, 
brownish,  etc. 
Pleochroic  green,  yellow.     Ir- 
regular 
Pleochroic  brown  or  colorless. 
Plates 
Plates,  pleochroic  in  greens 

Garnet, 

most  varieties 
Epidote 

Titanite 
Roscoelite 

49.   A. 

Crystal  System: 

Flame 

Name,  Composition,  Hardness 

Fusibility. 

Colora- 

Other Tests. 

Usual  Appearance. 

and  Specific  Gravity. 

tion. 

O.  Strontianite,  p.  436, 

5 

Crim- 

Sprouts  and 

White  or  tinted 

SrCO3 

son 

glows  intensely 

columnar   or 

H.,  3  to  3-5            Sp.  gr.,  3.7 

during  fusion 

compact 

M.   Barytocalcite,  p.  433, 

5(?) 

Yellow- 

Pale green  after 

White  or  tinted 

(Ba.Ca)CO 

ish 

fusion 

masses   and 

H.,  4                        Sp.  gr.,  3.6 

green 

crystals 

50.   A. 

—  .  Sepiolite,  p.  546, 

5 

Pink   ignited 

White   smooth 

H4Mg2Si3Oio 

with  Co.  Sol. 

feeling,    light 

H.,  2  to  2.5         Sp.  gr.,  i  to  2 

masses.    Rare- 

ly fibrous 

M.  Wollastonite,  p.  507, 

4 

Yellow- 

Often    efferves- 

White   to    gray 

CaSiOs 

red 

ces 

fibrous  to  com- 

H., 4  to  5      Sp.  gr.,  2.8  to  2.9 

pact   masses. 

Rarely  crystals 

Tri.  Anorthite,  p.  494, 

5 

Yellow- 

Cleavage  angle 

Colorless  or  gray 

CaAl2Si2O8 

red 

86° 

crystals   and 

H.,  6  to  6.5           Sp.  gr.,  2.75 

compact 

607 


51.   A. 


Crystal  System  : 
Name,  Composition,  Hardness 
and  Specific  Gravity. 

Fusibility 

Flame 
Colora- 
tion. 

Other  Tests. 

Usual  Appearance. 

M.  Biotite,  p.  540, 
(H.K)2(Mg.Fe)2  Al2(SiO4)3 
H.,  2.5  to  3             Sp.  gr.,  2.7 
—  .  Serpentine,  p.  544, 
H4Mg3Si2O9 
H.,  3  to  4      Sp.  gr.,  2.5  to  2.6 
H.  Apatite,  p.  470, 
Ca6(Cl.F)  (P04)3 
H.,  4.5  to  5        Sp.  gr.,  3.2 

T.  Scheelite,  p.  353,  CaWO4 
H.,  4.5  to  5    Sp.gr.,  5.9  to  6.  i 

O.  lolite,  p.  529, 
H2(Mg,Fe)4Al8Sii0037 
H.,  7  to  7.5             Sp.  gr.,  2.6 

5 

5  to  5.5 

5 
5 

5  to  5-5 

Yellow- 
ish red 

Pale  red 

Cleaves  to  thin 
elastic  plates 

Pink  if  ignited 
with  Co.  Sol. 

Easy   solution 
P.  test  p.  191 

S.    Ph.    0.    F. 
colorless   to 
white.     R.  F. 
deep  blue 

A  little  water  in 
closed  tube 

Black    "mica" 
rarely  in  large 
sheets 
Mottled  yellow, 
green,  -feeble 
lustre  or  silky 
Green,    red   and 
white  prisms. 
Resinous  lustre. 
White  compact 
Heavy  yellowish 
masses,    resin- 
ous   lustre. 
Square      pyra- 
mids 
Like    blue   or 
purple  quartz. 
Often  altered 

49.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  a-Monobrom- 
Naphthalin 

High  order 

Laths.     Ex.,  H.     El.  (—  ) 

Strontianite 

>  a-Monobrom- 
Naphthalin 

High  order 

Laths.     Ex.  Obi. 

Barytocalcite 

50.     B.                             (CRUSHED   FRAGMENTS.) 

<  Bromoform 

Gray  or  White 
Aggregate 
Gray  or  White 
to  Bright  A. 

Fibres.       Ex.,    ||.      El.    (+) 
or  irregular 
Laths.     Ex.,  35°—  40° 

Sepiolite 
Anorthite 

>  Bromoform 

Gray  or  White 

Laths   or    Needles.      Ex.,    ||. 
El.  (+) 

Wollastonite 

51.     B.                              (CRUSHED   FRAGMENTS.) 

<  Bromoform 

Gray  or  White. 
Aggregate 

Gray  or  White 
Gray  or  White 
to  Bright  A. 

Fibres.      Ex.,    |l.      El.    (+). 
or  irregular 

Pleochroic  if  colored 

Serpentine 

Chrysotile 
Antigorite 
Biotite 
lolite 

>  Bromoform 
<  Methylene 
Iodide 

Gray  or  White 

Irregular.     Ex.,  ||  cleavages 

Apatite 

: 

>  Methylene 
Iodide 

Bright  A. 

Irregular 

Scheelite 

608 

52.   A 


Crystal  System:  Name,  Composition, 
Hardness  and  Specific  Gravity. 


Fusibility. 


Other  Tests. 


Usual  Appearance. 


O.  Talc,  p.  545.  H2Mg3(SiO3)4 
H.,  i  to  i. 5      Sp.  gr.,  2.5  to  2.9 

— .  Pyrophyllite,  p.  548, 

HAl(Si03)2 

H.,  i  to  2        Sp.  gr.,  2.8  to  2.9 
Chlorite  Group,  p.  541, 
H.,  i  to  2. 5      Sp.  gr.,  2.6  to  2.9 


Mica  Group,  p.  537, 

H.,  2  to  3  Sp.  gr.,  2.7  to  3 


M.  Orthoclase,  p.  492, 

(or  Microcline),  KAlSisOs 
H.,  6  to  6.5    Sp.  gr.,  2.5  to  2.6 

O.  Enstatite-Hypersthene,   p. 
504,  (Mg.Fe)SiOs 

H.,  55  Sp.  gr.,  3.1  to  3-3 

O.  Anthophyllite,  p.  507, 

(MgFe)SiOs 

H.,  5. 5  to  6  Sp.gr.,  3^1  to  3. 2 
H.  Tourmaline,  p.  524, 

Ri8B2(Si05)4 

H.,  7  to  7.5  Sp.  gr.,  3  to  3.2 
H.  Beryl,  p.  522,  BesAUCSiOOe 
H.,  7. 5  to  8  Sp.  gr.,  2.6  to  2.8 


5  to  5.5 


5  to  5-5 


4  to  5 


5  to  6 
5  to  6 

5 
5  to  5-5 


Pink  with  Co.  Sol. 
Soapy  feeling 

Blue  with  Co.  Sol. 


Much  water  in 
closed  tube. 
Cleave  to  non- 
elastic  plates 

Water  at  high  heat 
closed  t  ube . 
Cleave  to  elastic 
plates 

Violet  flame  (color 
screen).  Cleavage 
90°.  Rarely 
striated 


After  fusion  is  mag- 
netic 

Green  Fl.  with  Bo. 
Fl.  After  fusion 
will  gelatinize 

Often  white  on  fu- 
sion 


White  greenish  or 
gray  foliated  com- 
pact and  fibrous 

Radiated  foliae  or 
fibres  and  compact 
masses 

Dark  green,  rarely 
red,  coarse  and 
fine  scales  and 
crystals 

Black,  amber,  gray, 
etc.,  scales  and 
pseudohexagonal 
crystals 

Flesh  red,  white, 
gray,  etc.  Cleav- 
ages and  crystals 
common 

Gray,  brown,  black 
lamellar  to  fibrous, 
pearly  metalloidal 

Gray  to  green  lamel- 
lar and  fibrous 

Red,  blue,  colorless, 

etc.,  prisms  often 

triangular 
Green,  yellow,  blue, 

hexagonal  prisms. 

Also  columnar 


52.    B. 


(CRUSHED   FRAGMENTS.) 


Index  of  Refraction.    Interference  Color. 


Other  Notable  Characters. 


Name. 


<  Bromoform 


Abnormal    blue 

or    blown    or 

gray 

Gray  or  White 
Gray  or  White 

to  Bright  A. 
Gray  or  White 

to  Bright  A. 

Bright  A. 

Gray  or  White 
to  Bright  A. 


Plates.     Biax.  I.  F.     Green. 
Pleochroic 

Irregular 

Laths.     Ex.,  ||  on  ooi,  5°  on 

oio 
Laths.     Ex.,   15°  on  ooi,   5° 

on  oio.     Crossed  twinning 

(grating) 
Irregular,    or    plates.     Biax. 

I.  F. 
Laths.     Ex.,  ||,  El.  (+) 


Chlorite  Group 
See  page  542 

Beryl 
Orthoclase 

Microcline 


Talc 

Pyrophyllite 


>  Bromoform 

<  tt-Monobrom- 
Naphthalin 


Gray  or  White 

or  Black 
Gray  or  White 

to  Bright  A. 


Plates.  Biax.  I.  F.  Distinc- 
tions p. 

Irregular.  Pleochroic  and 
colorless 


Mica  Group 
Tourmaline 


>  orMonobrom- 
Naphthalin 


Gray  or  White 
to  Bright  A. 


Bright  B. 


Laths    and    fibres.      Ex.,    ||. 

El.  (+).     Colorless 
Laths.       Ex.,     H,     El.     (+). 

Pleochroic  pink  to  green 
Fibres.     Ex.  ||.     El.  (+) 

609 


Enstatite 

Hypersthene 

Anthophyllite 


53.   A. 


—  .  Allophane,  549. 
Al2Si06.5H20 
H.,  3                        Sp.  gr.,  1.88 

Much 
water 

Crumbles    when 
heated 

Sky     blue,      green, 
brown   and   white 
crusts 

54.   A. 

M.  Aluminite,  p.  415, 
Al2SOn  +pH2O 
H.,  i  to  2                 Sp.  gr.,  1.6 
—  .  Bauxite,  p.  413,  A12O(OH)4 
H.,  i  to  3        Sp.  gr.,  2.4  to  2.5 

I.  Leucite,  p.  498,  KAl(SiO3)2 
H.,  5.5  to  6      Sp.gr.,  2.4  to  2.  5 
O.  Wavellite,  p.  471, 
A1»(OH)6(PO4)  4  +9H2O 
H.,  3  to  4                Sp.  gr.,  2.33 

Much 
water. 
S02 
Water  at 
high 
heat 

Acid 
water 
etches 

Infusible  with  soda 
but    mass    will 
stain  silver 
May  become  mag- 
netic in  R.  F. 

Violet    Fl.     (Color 
screen) 

White  chalky  with 
harsh  feel 

Rounded   grains   or 
earthy  or  clay-like 

Translucent    white, 
nearly    spherical 
Spheres   and   hemi- 
spheres of  radiat- 
ing crystals 

54.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  Xylol 

Gray  or  White 

Fibres.     Ex.,  Obi. 

Aluminite 

>  Xylol 
<  Bromoform 

Black  aggregate 
Gray  or  White 
or  Black. 
Bright  B. 

Irregular 
Irregular.     Twin  lamellae  in- 
clusions 
Rectangles  and  needles.     Ex., 
||.     El.  (+) 

Bauxite 
Leucite 

Wavellite 

55.   A. 


Crystal  System:  Name,  Composition. 
Hardness  and  Specific  Gravity. 

Closed 
Tube. 

Other  Tests. 

Usual  Appearance. 

M.  Kaolin,  p.  547,  H4Al2Si2O9 

Water 

Usually  plastic 

Dull    white,    mealy 

H.,  2  to  2.5               Sp.  gr.,  2.6 

unctuous 

M.  Gibbsite,  p.  415,  A1(OH)3 

Water 

Exfoliates 

Smooth    pearly 

H.,  2.5  to  3.5            Sp.  gr.,  2.4 

crusts  or  fibres 

H.  Alunite,  p.  416, 

Water  at 

Violet  Fl. 

Cub  ids  or  granular 

K(A103)  (S04)2+3H20 

red  heat 

or  fibrous.    White 

H.,  3.  5  to  4.5  Sp.gr.,  2.6  to  2.  7 

or  tinted 

Tri.  Cyanite,  p.  519,  Al2SiO5 

Softer    parallel 

Blue    blade-like. 

K.,sto7        Sp.  gr.,  3-6  to  3.7 

length 

Centre  bluest 

O.  Sillimanite,  p.  519,  Al2SiOs 

Very  tough 

Thin  gray  or  brown 

H.,  6  to  7                  Sp.  gr.,  3.2 

crystals  or  fibrous 

O.  Andalusite,  p.  518,  Al2SiO5 

Inclusions.     See  p. 

Gray  or  pink  nearly 

H.,  7  to  7.5      Sp.gr.,  3.  i  to  3.  2 

80 

square      prisms 

H.  Phenacite,  p.  567,  Be2SiO4 

Resembles  quartz 

Colorless    rhombo- 

H.,  7.5  to  8            Sp.  gr.,  2.96 

hedral  crystals 

O.  Diaspore,  p.  415,  AIO(OH) 

Water 

Pink  or  brown  foli- 

H., 6.5 

ated 

O.  Topaz,  p.  523,  Ali2Si6O2BFi0 

O.  T.  F. 

Easy   basal   cleav- 

Colorless, yellow 

H.,  8              Sp.  gr.,  3.4  to  3.6 

with 

age 

and    bluish    crys- 

S. Ph. 

tals.     Columnar 

I.  Spinel,  p.  558,  MgAl2O4 

Completely  soluble 

Red,     black,     etc., 

H.,  8               Sp.  gr.,  3.5  to  4.5 

S.  Ph. 

octahedra 

O.  Chrysoberyl,  560,   BeAl2O4 

Tabular  and  twin- 

Pale to  deep  green 

H.,  8.5           Sp.  gr.,  3.5  to  3..8 

ned 

crystals 

H.  Corundum,  p.  412,  A12O3 

Nearly  cubic  part- 

Gray, blue,  red,  etc. 

H-,  9              Sp.  gr.,  3.9  to  4.1 

ing  striations 

crystals 

610 


55.     B.              (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  Bromoform 

Gray  or  White. 
Aggregate 
Gray  or  White. 
Aggregate 
Gray  or  White 
or  Black 

Irregular  and  plates.     Cloudy 
Plates 

Three  or  six-sided  with  Uniax. 
I.  F.  or  irregular 

Kaolinite 
Gibbsite 
Alunite 

>  Bromoform 
<  cc-Monobrom- 
Naphthalin 

Gray  or  White 
Gray  or  White 
to  Bright  A. 

Plates  with  Biax.  I.  F.  and 
irregular 
Irregular  or  laths  with  Ex.  || 

Topaz 

Andalusite 

>  a-Monobrom- 
Naphthalin 

<  Methylene 
Iodide 

Black 

Gray  or  White 
to  Bright  A. 
Gray  or  White 
to  Bright  A. 
Bright  A. 

Bright  B. 

Irregular.      Tinted    green   or 
brown 
Irregular 

Laths.      Cross  cracks.      Ex. 
30°.     El.  (+) 
Laths   or   Needles.      Ex.     ||. 
El.  (+) 
Laths.     Ex.  |1.     El.  (—  ). 

Spinel 
Phenacite 
Cyanite 

Sillimanite 
Diaspore 

>  Methylene 
Iodide 

Gray  or  White 
to  Bright  A. 
Gray  or  White 
to  Bright  A. 

Irregular,  green  or  colorless 
Irregular 

Chrysoberyl 
Corundum 

56.    A. 


Crystal  System:  Name,  Composition, 
Hardness  and  Specific  Gravity. 

Fragments 
in  HC1. 

With  Cobalt  Solution. 

Usual  Appearance. 

H.  Calcite,  p.  446,  CaCOs 

Rapid  eff  . 

Unchanged  on  boil- 

White,   yellowish, 

H.,  3                          Sp.  gr.,  2.7 

cold 

ing 

etc.,   crystals  and 

granular   (marble) 

O.  Aragonite,  p.  444,  CaCOs 

Rapid  eff. 

Lilac  on  boiling 

White,    yellowish, 

H.f  3.5  to  4              Sp.  gr.,  2.9 

cold 

prisms,     needles, 

fibres  coral-like 

H.  Dolomite,  p.  448, 

Slow  eff. 

Pink  on  ignition 

White    or    pink 

CaMg(C03)2 

cold 

curved  rhombohe- 

H.,  3.  5  to  4      Sp.gr.,  2.  8  to  2.  9 

drons,  granular 

H.  Magnesite,  p.  453,  MgCOs 

Very  slow 

Pink  on  ignifion 

White  nodules  shell- 

H.,  3.  5  to  4.5      Sp.gr.,  3  to  3.  i 

eff.  cold 

like   fracture   also 

cleavable 

H.  Rhodochrosite,  p.  284, 

Very  slow 

Unaffected 

Pink  to  red  curved 

MnCOs 

eff.  cold 

rhombohedrons  or 

H.,  4.5            Sp.  gr.,  3.5  to  4.5 

massive 

56.     B.             (CRUSHED   FRAGMENTS.) 

Index  of 
Refraction.* 

Interference 
Color. 

Other  Notable  Characters. 

Name. 

High  Order 

Plates  or  laths.     Ex.  ||.      El., 

Aragonite 

<  a-Monobrom- 
Naphthalin 

High  Order 

Rhombs.      Striations   ||    long 
diagonal.     Ex.  Sym. 

Calcite 

>  orMonobrom- 
Naphthalin 

High  Order 
High  Order 
High  Order 

Rhombs.     Ex.  Sym. 
Rhombs.     Ex.  Sym. 
Rhombs.     Ex.  Sym. 

Dolomite 
Magnesite 
Rhodochrosite 

*  All  except  aragonite  cleave  to  rhombohedrons  of  105°  to  107°. 

*  These  are  parallel  short  diagonal.     The  indices  parallel  the  long  diagonal  are 
notably  larger  by  0.17  to  0.22. 

6n 


57.   A. 


Crystal  System:  Name,  Composition, 
Hardness,  and  Specific  Gravity. 

Closed 
Tube. 

Other  Tests. 

Appearance. 

Cerite,  p.  351.  Ce.,  etc.,  Si. 
H.f  5.5                      Sp.  gr.,  4.9 

T.  Thorite,  p.  315.  ThSiO4 
H.,  5              Sp.  gr.,  4.8  to  5-2 
O.  Chrysolite,  p.  513, 
(MgFe)2Si04 
H.,  6.5  to  7      Sp.gr.,  3.3  to  3-6 
O.  Forsterite,  p.  513.  Mg2SiO4 
H.,  6  to  7       Sp.  gr.,  3.2  to  3.3 

Water 

Water 

Whitens 

Whitens 

In  forceps.    Yellow 
In  borax  dark  yel- 
low O.  F.  hot 
High  sp.  gr.     Usu- 
ally altered 
In  forceps  whitens 

Brown  to  cherry  red 
massive.  Resinous 

Orange    to    brown, 
zircon  shaped 
Olive  to  gray  green 
glassy  grains  and 
masses  of  grains 
White     or     yellow 
grains  or  crystals 

58.   A. 


Garnierite,  p.  294, 

Blackens. 

Borax  O.  F.  violet 

Emerald-  and  pale- 

H2(Ni.Mg)SiO4+H2O 

Yields 

hot,  brown  cold 

green  and  cellular 

H.,  2  to  3      Sp.  gr.,  2.3  to  2.8 

water 

masses  and  crusts. 

—  .  Chrysocolla,  p.  372, 

Blackens. 

With  soda  on  coal 

Enamel  -like  crusts, 

CuSiO3.2H2O 

Yields 

a  copper  button. 

veins  or  compact 

H.,  2  to  4          Sp.  gr.,  2  to  2.3 

water 

Emerald  green  Fl. 

H.  Brucite,  p.  452,  Mg(OH)2 

Water 

Pink  with  Co.  Sol. 

White    foliated     or 

H.,  2.5                      Sp.  gr.,  2.4 

fibrous.      Pearly 

O.  Cervantite,  p.  335,  Sb2O4 

Easily  reduced   on 

Yellow  to  white  dull 

H.,  4  to  5                 Sp.  gr.,  4.1 

charcoal 

or  pearly 

M.  Monazite,  p.  313, 

Reflected  light  with  spectro- 

Resinous   brown 

(Ce.La.Di)PO4 

scope   gives   broad   line   be- 

crystals or  yellow 

H.,  5  to  5.5      Sp.  gr.,  4.9  to  5.3 

tween  the  red  and  yellow  and 

grains 

narrow  line  in  the  green 

Turquois,  p.  570, 

Blackens. 

P  test  see  p.   191. 

Sky-blue    to    green 

A12(OH)3P04H20 

Yields 

Blue  Fl.  with  HC1 

nearly    opaque 

H.,  6              Sp.  gr.,  2.6  to  2.8 

water 

with  lustre  of  wax 

M.  Gadolinite,  p.  315, 

Unaltered 

Swells,  cracks  and 

Rough    green    to 

Yt2Be2FeSi2Oio 

often  glows 

black  prisms 

H.,  6.5  to  7              Sp.  gr.,  4.3 

57.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  a-Monobrom- 
Naphthalin 

Bright  A. 

Irregular.     Colorless  or  pleo- 
chroic  yellow 

Chondrodite 

>  a-Monobrom- 
Naphthalin 

Bright  B. 
Bright  B. 

Irregular,  colorless,  yellow 
Irregular.     Colorless 

Chrysolite 

Forsterite 

>  Methylene 
Iodide 

Black 

Often  isotropic 

Thorite 

58.   B. 


(CRUSHED   FRAGMENTS.) 


<  Bromoform 

Black  or  Gray 
or  White 
Black    or    Ag- 
gregate 

Plates,  Uniax.  I.  F.     Fibres, 
Ex.  ||.     El.  (—  ) 
Irregular.    Pale  blue  or  green 

Brucite 
Chrysocolla 

=  Bromoform 

Gray  or  White 
Aggregate 

Irregular.     Greenish 

Garnierite 

>  Bromoform 

Gray  or  White 
Aggregate 
Bright  B. 

Irregular 
Plates.     Faint  yellow 

Turquois 

Monazite 

>  Methylene 
Iodide 

Varies  Black  to 
high  order 

Normally    anisotropic,    often 
isotropic 

Gadolinite 

612 


59.   A. 


Crystal  System:  Name,  Composition, 
Hardness  and  Specific  Gravity. 

Other  Tests. 

Usual  Appearance. 

T.  Xenotime,  p.  313,  YPO4 

Test  P.  p.  191 

Zircon-like  crystals,  brown 

H.,  4  to  5                  Sp.  gr.,  4.5 

or  yellow  in  color 

T.  Fergusonite,  p.  356, 

Test  Cb  p.  1  86 

Brownish  black  resinous 

Cb,  TaYCe,  etc. 

H.,  5.5  to  6              Sp.  gr.,  5.8 

—  .  Opal,  p.  487,  SiO2nH2O 

In  closed  tube.    A  little 

No   crystals.    Translucent. 

H.,  5.  5  to  6.5  Sp.gr.,  2.  i  to  2.  2 

water  becomes  opaque 

May  be  any  color,  opaque 

Rarely  play  of  colors 

and  dull 

T.  Rutile,  p.  309,  TiO2 

S.   Ph.   0.   F.   yellow, 

Brownish     red     to     black 

H.,  6  to  6.  5      Sp.gr.,  4.1  to  4.2 

made  violet  R.  F. 

hairs  to  coarse  crystals 

Chalcedony,  p.  486,  SiOa 

No  crystals 

"Tendon"  colored,  red,  blu- 

H., 6.5                       Sp.  gr.,  2.6 

ish,  etc.     Lustre  wax-like 

H.   Quartz,  p.  484,  SiO2 

Horizontal     striations 

Prisms  with  rhombohedra. 

H.,  7                        Sp.  gr.,  2.65 

on  prisms 

Also     massive.     Colorless 

and  all  colors 

H.  Tridymite,  p.  486,  SiO2 

Minute  tabular  and  twinned 

H.,  7                          Sp.  gr.,  2.3 

crystals 

I.  Garnet,  p.  510,  Uvarovite, 

Green  bead  with  S.  Ph. 

Emerald     green,      dodeca- 

Ca3Cr2(SiO4)3 

hedrons 

H.,  7.5           Sp.  gr.,  3.1  to  4.3 

T.  Zircon,  p.  314,  ZrSiO4 

Glows     intensely     on 

Sharp  square  pyramid  and 

H.,  7.5                       Sp.  gr.,  4.7 

heating.    Adamantine 

prism   brown,   gray,    red. 

lustre 

etc.     Also  pebbles 

O.  Staurolite,  p.  520, 

Dark  brown,  usually  twin- 

Fe(A10)4(A10H)(Si04) 

ned  (cross)  prisms  at  90° 

H.,  7.5           Sp.  gr.,  3-6  to  3-7 

and  120° 

H.  Tourmaline,  p.  524, 

Green    flame    with 

Transparent    deep    red 

(Rubellite)     Ri3B2(SiOB)4 

KHSCu     CaF2 

prisms 

H.,  7  to  7.5        Sp.  gr.,  3  to  3.2 

I.   Diamond,  p.  550,  C 

In   powder   is   burned 

Colorless  and  tinted  octa- 

H.,  10                      Sp.  gr.,  3.51 

to  CO2.     Cleavages  at 

hedra  with  rounded  edges. 

70°  31'. 

Lustre  like  oiled  glass 

59.     B.             (CRUSHED   FRAGMENTS.) 

Name. 

Index  of 
Refraction. 

Interference 
Color. 

Other  Notable  Characters. 

<  Xylol 

Black 
Gray  or  White 

Irregular 
Plates.     Twinned 

Opal 

Tridymite 

>  Xylol 
<  Bromoform 

Gray  or  White 
to  Bright  A. 
Gray  or  White 
to  Bright  A. 

Irregular 

Irregular.      Fibrous    with 
crossed  Nicols 

Quartz 

Chalcedony 

>  Bromoform 
<  a-Monobrom- 
Naphthalin 

Gray  or  White 
to  Bright  A. 

Irregular.     Red,  pleochroic 

Tourmaline, 

(Rubellite) 

=  Methylene 
Iodide 

Gray  or  White 

Irregular.      Pleochroic.      In- 
clusions 

Staurolite 

>  Methylene 
Iodide 

Black 

Black 
Bright  B. 
High  Order 
High  Order 

Irregular.     Pink 

Irregular 
Irregular 

Irregular.     Yellow  to  reddish 

Garnet, 
(Uvarovite) 
Diamond 
Zircon 
Xenotime 
Rutile 

613 


INTERNATIONAL   ATOMIC   WEIGHTS. 


0  =  16.  H  =  l. 

Aluminium Al  27.1       26.9  Neodymium.   .  .  Ne 

Antimony Sb  120.2     119.3  Neon 

Argon A  39.9       39.6  Nickel     .    .    .    .  Ni 

Arsenic As        75.0       74.4  Nitrogen     .    .    .  N 

Barium Ba  137.4     136.4  Osmium .    .    .    .  Os 

Beryllium  (Glucinum)  .  Be  9.1          9.03  Oxygen.    .    .    .O 

Bismuth Bi  208.5     206.9  Palladium.    .    .  Pd 

Boron B          II  10.9  Phosphorus    .    .  P 

Bromine Br         79-96     79-36  Platinum    .    .    .  Pt 

Cadmium Cd  112.4     ni-6  Potassium  .    .    .  K 

Caesium Cs  133          132  Praseodymium  .  Pr 

Calcium Ca  40.1        39.8  Radium.    .    .    .  Ra 

Carbon C  12.00      11.91  Rhodium    .    .    .  Rh 

Cerium Ce  140         139  Rubidium  .    .    .  Rb 

Chlorine Cl  35-45      35- 18  Ruthenium.   .    .  Ru 

Chromium Cr  52.1        51.7  Samarium  .    .    .  Sm 

Cobalt Co  59.0       58.56  Scandium.  .    .    .  Sc 

Columbium  (Niobium).  Cb  94  93.3  Selenium.    .    .    .  Se 

Copper    .......  Cu  63.6       63.1  Silicon    ....  Si 

Erbium E  166        164.8  Silver Ag 

Fluorine F  19  18.9  Sodium   .    .    .    .  Na 

Gadolinium Gd  156        155  Strontium   .    .    .  Sr 

Gallium Ga         70          69.5  Sulphur  .    .    .    .  S 

Germanium Ge  72.5       71.9  Tantalum    .    .    .  Ta 

Gold Au  197.2      195.7  Tellurium  .    .    .  Te 

Helium He         4  4  Terbium Tb 

Hydrogen H  1.008     i.ooo  Thallium    .    .    .  Tl 

Indium In  114         113.1  Thorium.    .    .    .  Th 

Iodine I  126.85   125.90  Thulium.    .    .    .  Tm 

Iridium  ...     .   .    .    .  Ir  193.0     191.5  Tin Sn 

Iron Fe  55.9       55.5  Titanium.    .    .    .  Ti 

Krypton Kr  81.8       81.2  Tungsten    .    .    .W 

Lanthanum La  138.9     137.9  Uranium.    .    .    .  U 

Lead Pb  206.9     205.35  Vanadium  ...  V 

Lithium Li  7.03       6.98  Xenon    ....  X 

Magnesium Mg  24.36     24.18  Ytterbium  .    .    .  Yb 

Manganese Mn  55.0       54.6  Yttrium.    .    .    .  Yt 

Mercury Hg  200.0     198.5  Zinc Zn 

Molybdenum Mo        96.0      95.3  Zirconium.    .    .  Zr 

614 


0  =  16. 

143.6 

20 

58.7 
14-04 

16.00 
106.5 

31.0 
194.8 

39-15 

140.5 

225 

103.0 
85.4 

101.7 

150 
44.1 
79.2 
28.4 

107.93 

23-05 

87.6 

32.06 

183 
127.6 
1 60 
204.1 

232-5 
171 
119.0 
48.1 
184.0 

238.5 
51.2 

128 

173.0 
89.0 

65.4 
90.6 


H=l. 

142.5 

19.9 

58.3 

189.6 
15.80 

105.7 
30.77 

J93-3 
38.86 

139-4 
223.3 

102.2 

84.8 
IOO.9 
148.9 

43-8 
78.6 
28.2 

IO7.  12 

22.88 

86.94 
31.83 

181.6 
126.6 
158.8 
202. 6 
230.8 
169.7 
118.1 

47-7 
182.6 

236.7 
50.8 

127 

171.7 
88.3 
64.9 
89-9 


GENERAL  INDEX. 


Abnormal  interference  colors,  138 
Absorption  in  crystals,  99,  104,  151 

spectra,  169 
Acids,  definition,  236 
Acute  bisectrix,  107,  143 
Adamantine  lustre,  210 
Adjustment  of  goniometer,  83 

of  microscope,  122,  123 
Adsorption,  235 
Aggregates,  crystal,  70 

shape  and  grouping,  70 
Alterations,  chemical,  236,  239,  240 
Aluminum,  hydrous  silicates,  547 

silicates,  517 

summary  of  tests,  182 

see  also,  173,  202,  206 
Aluminum  minerals,  406 

uses  and  extraction,  408 
Ammonium,  test,  182 
Ammonium  minerals,  430 
Amorphous  condition,  209 
Amygdaloidal,  74 
Analyzer  of  microscope,  118 
Angle  between  optic  axes,  107,  147,  149 
Angles,  3 

apparent  with  microscope,  148 

approximate,  5,  12 

changed  by  expansion,  226 

critical,  no 

extinction,  138 

measurement  of  interfacial,  3,  82 

of  hexagonal  crystals,  16 

of  isometric  crystals,  67 

of  monoclinic  crystals,  19 

of  orthorhombic  crystals,  17 

of  tetragonal  crystal?,  15 

of  triclinic  crystals,  20 

opening,  no 

Anisotropic  crystals,  100,  127 
Antimony,  summary  of  tests,  182 

see  also,  171,  172,  176,  197,  198,  199, 

200 
Antimony  minerals,  332 

uses  and  extraction,  332 

formation  and  occurrence,  333 
Anvil,  160 
Apparatus,  156 
Arborescent,  74 
Arsenic,  summary  of  tests,  183 

see  also,  171,  172,  173,  176,  197,  205 
Arsenic  minerals,  327 

economic  importance,  328 


Arsenic   minerals,  formation   and  occur- 
rence, 328 
Associates,  239 
Asterism,  211 

Atomic  weights,  table  of,  614 
Axes,  crystallographic,  20 

choosing,  20,  29,  32,  37,  43,  49,  52, 
55,  58,  62,  65 

interchangeable,  21 

of  symmetry,  7,  8,  10 

of  the  six  systems,  21 

optic,  102 
Axial  angle,  optic,  107 

measurement,  147,  149 

changed  by  heat,  229 
Axial  cross,  construction,  93 

elements,  calculation  of,  91 

Balance,  219 

Jolly,  220 

Kraus- Jolly,  221 

Westphal,  224 
Barium,  summary  of  tests,  173 

(see  also  202,  205,  207) 
Barium  minerals,  431 

uses  and  production  of,  431 

formation  and  occurrence,  432 
Bar  theory,  255,  419 
Basal  pinacoid,  30,  34,  39,  44,  49,  56 

plane,  53 
Basalt,  479 
Bases,  definition,  236 
Basic  lava  flows,  copper  inr  361 
Beads,  how  to  make,  162 
Bead  tests,  177 

table  of,  179 
Becke  line,  128 
Beryllium  minerals,  562 
Berzelius  lamp,  157 
Biaxial  crystals,  105 

interference  figure,  140,  143,  145 

ray  surface,  105 
Birefringence,  104,  107 

determining,  135,  137 
Bisectrix,  acute  and  obtuse,  107,  143 
Bismuth,  summary  of  tests,  184 

see  also,  171,  172,  173,  176,  178,  199, 

200 
Bismuth  minerals,  324 

formation  and  occurrence,  325 

uses  and  extraction,  325 
Bismuth-flux,  172 


615 


6i6 


GENERAL   INDEX. 


Bladed,  71 

Blast,  method  of  blowing,  161 

Blowpipe  analysis,  scheme  for,  197 

operations  of,  154 
Blowpipe  apparatus,  157 
Blowpipe,  description  of,  157 
Blowpipe  lamps,  158 
Blowpipe  tests,  summary  of,  182 

advantages  of,  156 
Bluestone,  480 
Boracic  acid  flux,  184 
Borax,  reactions  with,  177,  179 

how  to  make  bead,  162 
Borax  lakes,  minerals  of,  255,  456 
Boron,  summary  of  tests,  184 

see  also,  205,  206 
Boron  minerals  and  their  uses,  454 

formation  and  occurrence  455 
Botryoidal,  74 
Brachy  dome,  39 

pinacoid,  30,  39 

pyramid,  38 
Brass,  296,  359 
Braun's  solution,  224 
Bravais  double  plate,  137 
Brittle,  216 
Bromine,  summary  of  tests,  184 

see  also,  175,  203,  459 
Bronze,  304,  359 
Building  stones,  479 
Bunsen  burner,  156 

Cadmium  borotungstate  solution,  224 

mineral,  293 

source  and  use,  296 

summary  of  tests,  185 

see  also,  173,  176,  180,  198 
Calcite,  double  refraction  in,  100 
Calcium  minerals,  437 

formation  and  occurrence,   438 

see  also,  169,  173,  202,  205,  207 

summary  of  tests,  185 

uses  and  production,  437 
Carbonated  water,  solvent  power,  243 
Carbonates,  425  , 

from  spring  waters,  254 
Carbon  minerals,  472 

economic  importance,  473 

formation  'and  occurrence,  475 
Carbon  dioxide,  summary  of  tests,  105 

see  also,  204,  205 

Cements,  see  hydraulic  cements,  324 
Centering  of  goniometer,  83 

of  microscope,  123 
Center  of  symmetry,  7,  10 
Cerium  minerals,  310 
Cerium  production  and  uses,  311 
Change  of  color,  211 
Character,  optical,  103,  107,  145 
Charcoal,  method  of  using,  169 

reactions  obtained  on,  171 


Chart,  spectroscopic,  168 
Chemical  alterations,  236,  239 

balance  for  sp.  gr.,  219 

composition,  208,  231 

characters,  240 

sediments,  248,  253 

types,  236 
Chlorine,  summary  of  tests,  185 

see  also,  459 
Chromium,  minerals,  346 

see  also  176,  179,  201 

uses  and  production,  346 

formation  and  occurrence,  346 

summary  of  tests,  185 
Circular  polarization,  104 
Characteristics,  isometric  crystals,  13 

hexagonal  crystals,  15 

orthorhombic  crystals,  16 

monoclinic  crystals,  17 

tetragonal  crystals,  14 

triclinic  crystals,  19 
Classification  of  crystals,  n 
Cleavage,  13,  213 
Clino  dome,  33 

pinacoid,  34 

Clinographic  projection,  92 
Closed  tubes,  reactions  in,  175 
Coal,  478 
Cobalt,  173,  179,  198,  202 

summary  of  tests,  186 
Cobalt  minerals,  286 

uses  and  production,  286 

formation  and  occurrence,  288 
Coefficients  of  Weiss,  22 
Color,  causes  of,  151,  155 

changes  in  closed  tubes,  176 
Color  screen,  Merwin's,  165 

scale,  interference,  196 

terms,  138 

Colloids,  81,  209,  235 
Coloration  of  flame,  165 
Colors,  interference,  114 
Columbium  minerals,  554 

tests,  1 86 
Columnar,  71 

Compensating  wedges,  136 
Composition  of  minerals,  208 
Conchoidal,  216 
Conductivity  of  heat,  226 

electrical,  229 
Conglomerates,  247,  398 
Constants  of  crystals,  82,  91,  107 
Contact  goniometers,  3 

minerals,  256 

twins,  68 

Convergent  polarized  light,  140 
Copper,  in  basic  lava,  361 

summary  of  tests,  186 

see  also,  173,  176,  179,  199,  202 
Copper  minerals,  357 

formation  and  occurrence,  359 


GENERAL   INDEX. 


6l7 


Copper  uses,  production  and  extraction, 

357 

Coralloidal,  74 

Corresponding  faces,  7,  12,  23 
Crossed  nicols,  no 
Crystal  aggregates,  70 

constants,  determination,  82 

definition,  i 

drawing,  92 

systems,  21 

condition,  209 

structure,  26,  208 
Crystallites,  77 
Crystallization,  2 

from  magma,  241 

from  solution,  243 

water  of,  237 
Crystallographic  axes,  20 
Crystallo-optics,  96  to  155 
Crystals,  angles  of,  3 

biaxial,  105 

classification,  n 

curved  faces,  78 

definition,  i,  2 

embedded,  74 

forms,  23 

grouping,  68 

growth  of,  74 

habit,  74,  75 

inclusions,  79 

irregularities  of  faces,  77 

isotropic,  99 

laws  of  3,7,  9,  24 

measurement  of,  5,  82 

models,  10 

negative,  80 

parallel  growth,  71,  8 1 

positive  and  negative,  103,  107 

sections,  125 

skeleton,  77 

striations,  77 

symmetry  of,  6  to  II,  87 

twin,  68 

uniaxial,  102 
Cube,  60 

Cupel  holder,  160,  379 
Cupellation,  test  for  silver,  378 
Curved  faces  of  crystals,  78 
Cutting  diamonds,  553 

Definite  chemical  composition,  208 
Deltohedron,  63 
Dendritic,  74 
Depolarization,  in 
Destructive  interference,  112 
Diamagnetism,  228 
Dichroscope,  154 
Dichroscopic  ocular,  154 
Diffusion  columns,  225 
Dihexagonal  pyramid,  55 
prism,  50 


Diploid,  65 

Dispersion  of  light,  98 
Ditetragonal  prism,  38,  44 

pyramid,  43 
Ditrigonal  prism,  53 
Dodecahedron,  60 
Domes,  30,  33,  39 
Double  magnetism,  228 
Double  refraction,  102,  107 

strength  of,  104 
Drawing  crystals,  92 
Drusy,  72 
Ductile,  216 
Dull  in  lustre,  210 

Earth's  crust,  208,  239 

Economic    importance,    see    under    eacJ 

group. 

Edges,  direction  of,  3,  94 
Elastic,  215 
Elasticity,  215 
Elements,  axial,  91 

principal,  239 
Electrical  characters,  228 

conductivity,  229 
Elongation,  sign  of,  134 
Embedded  crystals,  74 
Empirical  formulas,  231 
Equivalent  faces,  7,  12,  23 
Eruptive  rocks,  246 
Etched  crystals,  78 
Etching  figures,  28 
Eutecticum,  242 
Evaporation,  245 
Exhalations,  minerals  due  to,  252 
Expansion  of  by  heat,  226 

change  of  angle  by,  226 

change  of  optical  characters  by,  227 
Extinction  between  crossed  nicols,    no, 

139 
Extinction  angles,  138 

Faces,  corresponding,  7,  12,  23 

curved,  78 

elemental  or  parametral,  87,  88 

false  or  apparent,  78 

irregularities,  77 

roughened,  78 

striated,  77 

symbols,  21 

vicinal,  78 
Faster  and  slower  ray,  134 
Federow  universal  stage,  149 
Feel,  terms  used,  226 
Ferrochrome,  346 
Ferro-manganese,  277 
Ferrotitanium,  308 
Fibrous,  71 
Flame  colorations,  165 

oxidizing,  161 

reducing,  162 


6i8 


GENERAL   INDEX. 


Flame  structure  of,  161 

Flaming,  180 

Fletcher  lamp,  159 

Flexible,  215 

Fluorescence,  212 

Fluorine,  summary  of  tests,  187 

see  also  175,  182,  204,  459,  460 
Focusing  a  microscope,  123 
Foliated,  71 
Forceps,  160 
Form,  ideal,  10 
Formation  of  minerals,  see  mineral  forma- 
tion (and  under  each  group) 
Forms,  combinations  of,  23 

definition,  23 

possible  on  a  crystal,  27 

symbols  of,  23 
Formulas  of  minerals,  determining,  231, 
234 

empirical,  231 
Fracture,  216 
Frictional  electricity,  228 
Fuess  goniometer,  82 

microscope,  120,  125 

refractometer,  131 
Fusibility,  scale  of,  164 
Fusion,  165 
Fusion-solutions,  242 

Gabbro,  251 

Gangue  minerals,  259 

Gases  in  mineral  formation,  242,  243 

Gas  blowpipe,  158 

Gel  minerals,  208,  209,  235 

Gems,  550 

Genesis  of  minerals,  239-260 

Geode,  74 

Geometrical  constants,  82 

crystallography,  2 
Geometric  symmetry,  10 
German  silver,  287 
Glasses,  81,  209 
Gold,  tests  for,  173 
Gold  minerals,  392 

economic  importance,  393 

formation  and  occurrence,  394 
Goniometers,  contact,  3 

Fuess',  82 
Gneiss,  249 
Granular,  71 
Granite,  247,  256,  479 
Graphic  determination  of  indices,  89 
Greasy  lustre,  210 

Ground  water,  see  underground  water 
Grouping  of  crystals,  68,  71 
Growth  of  crystals,  74 
Guano  beds,  469 
Gypsum  test  plate,  137,  146 

Habit  of  crystals,  74,  75 
Hackly  fracture,  216 


53 


Hammer.  160 
Hand-goniometers,  3 
Hardness,  216 

scale  of,  217 
Heat,  conductivity,  226 

expansion,  226 
Heat  rays,  transmission,  226 
Heating  power  of  flame,  164 
Heavy  liquids,  use  of,  223 
Hemi  prism,  etc.,  30,  33 
Hemimorphic  ditrigonal  pyramid,  etc., 
Hexagonal  crystals,  angles,  16 

axial  elements,  91 

characteristics,  15 

classes,  48  to  57 

forms,  48  to  57 

optical  tests,  150 
Hexahedron,  60 
Hextetrahedron,  63 
Hexoctahedron,  58 
Hollow  crystals,  77 
Homogeneous  mixed  crystals,  234 
Hot  springs,  455,  462 
Hour  glass  structure,  79 
Hydrochloric  acid,  solubility  in,  180 
Hydrofluoric  acid,  solubility  in,  181 
Hydrogen  minerals,  465 
Hydroxides,  236 


Ideal  forms,  10 
Igneous  rocks,  246 

minerals  in,  305,  309,  312,  348,  439 
Illuminating  system,  117 
Image  in  microscope,  121 
Imitations  lapis  lazuli,  577 

turquois,  571 
Imperfections  of  crystals,  68 
Inclusions  in  crystals,  79 
Indices  of  Miller,  22 

graphic  determination,  89 
Indices  of  refraction,  97,  99,  103,  104,  107 

measurements  of,  127 

by  Becke  line,  128 

by  Due  de  Chaulnes  method,  131 

by  oblique  illumination,  129 

by  refractometers,  132 

by  Van  der  Kolk  method,  129 

with  liquids,  128 
Indices  zonal,  88 
nterchangeable  axes,  21 
nterfacial  angles,    measurement,  5,  82, 

87 

ntergrowths,  81 

nterference  of  monochromatic  light  be- 
tween crossed  nicols,  112 

colors  with  white  light,  114 
abnormal,  138 

color  scale,  116 

destructive,  112 

figures,  140,  141,  143,  145 
ntercepts,  21 


GENERAL   INDEX. 


619 


Internal  peculiarities,  79 

Inversion  points,  227 

Iodine,  summary  of  tests,  187 

see  also,  123,  175,  203,  460 
Iridescence,  definition,  211 
Iridium  minerals,  401 
Iridium,  uses*  402 

formation  and  occurrence,  404 
Iron,  summary  of  tests,  188 

see  also,  173,  176,  179,  198,  200,202 
Iron  minerals,  261 

extraction,  262 

economic  importance,  262 

formation  and  occurrence,  263 
Irregularities  of  crystal  faces,  77 
Isochromatic  curves,  144 
Isogyres,  143 
Isometric  crystals  angles,  13,  67 

classes  and  forms,  58  to  66 

characteristics,  13 

in  polarized  light,  99,  127 
Isomorphism,  232 
Isomorphous  mixtures,  233,  234 

substances,  232 
Isotropic  crystals,  99,  127,  141 

Jolly's  balance,  use  of,  220 
Klein's  solution,  224 
v.  Kobell's  scale  of  fusibility,  163 
Kraus  Jolly  balance,  221 

Lakes,  minerals  formed  in,  255,  455 

Lamellar,  71 

Lamps,  blowpipe,  158 

Law  of  constancy  of  interfacial  angles,  3 

of  simple  mathematical  ratio,  24 

of  symmetry,  7,  9 
Lead,  summary  of  tests,  188 

see  also,  171,  172,  173,  176,  199,  200 
Lead  minerals,  316 

formation  and  occurrence,  317 

uses,  production  and  extraction,  316, 

317 
Light,  dispersion,  98 

monochromatic,  99 

plane  polarized,  107 

transmission,  96 

vibrations,  96,  101 
Limestone,  248 

Liquids  for  indices  of  icfraction,  128 
Lithium,  summary  of  tests,  189 

see  also,  169,  205 

Lithium  minerals,   uses  and  production, 
428 

formation  and  occurrence,  428 
Lustre,  210 

Macro  dome,  etc.,  30,  39 
Magma,  minerals  of,  249 

see  also  silicate  groups 

molten  silicate,  241 


Magnesium,  summary  of  tests,  189 

hydrous  silicates,  543 
Magnesium,  see  also,  153,  181,  202,  206 
Magnesium  minerals,  449 

economic  importance,  450 
formation  and  occurrence,  451 
Magmatic    segregations,    251,    263,    289, 

308,  346,  360,  404,  410,  468 
Magnetic  characters,  227 
Magnetism,  228 
Magnification,  124 
Malleable,  216 
Mammillary,  74 
Manganese,  summary  of  tests,  189 

see  also,  179,  201 
Manganese  minerals,  277 

uses  and  production  of,  277 
formation  and  occurrence,  277 
Manganiferous  ores,  280 
Marine  borates,  456 
Marine  sediments  (phosphates),  469 
Marshes,  456 

Mathematical  ratio,  law  of,  24 
Measurement  of  interfacial  angles,  5,  82 
Mechanical  sediments,  247,  253 
Melting  points,  227 
Mercury,  summary  of  tests,  190 
see  also,  172,  176,  200,  205 
Mercury  minerals,  373 

economic  importance,  373 
formation  and  occurrence,  374 
uses,  production  and  extraction,  373 
Merwin's  color  screen,  165 
Metallic  lustre,  210 
Metasomatic  replacement,  245 

(see  Replacements) 
Metamorphic  rocks,  248 

minerals  in,  257,  and  group  discus- 
sions 

Micaceous,  71 
Mica  schist,  248 
Mica  test  plate,  135,  146 
Microchemical  methods,  238 
Microlites,  77 
Microscope,  adjustments,  122,  123 

polarizing,  117,  119,  120,  125,  148 
testing  with,  127 
Miller's  indices,  22 
Mineral  formation,  241,  349 

chemical  sediments,  253 

contacts,  256 

in  magma,  249 

magmatic  segregations,  251 

mechanical  sediments,  253 

oceans,  254 

pegmatites,  250 

regional  metamorphism,  257 

replacements,  256 

running  streams,  254 

springs,  253 

veins,  258 


620 


GENERAL   INDEX. 


Mineral  formation,  near  volcanoes,  252 

weathering,  252 

Mineral    occurrence,     (See    under    each 
group) 

synthesis,  240 
Mineralizers,  242 
Mineralogy,  definition,  209 
Mineral,  definition,  208 
Minerals,  iron,  etc.,  see  Iron  minerals,  etc. 
Mixed  crystals,  234 
Models  of  crystals,  10 
Moh's  scale  of  hardness,  217 
Molybdenum  summary  of  tests,  190 

see  also,  162,  171,  172,  173.  i?4.  2O1' 

205 
Molybdenum  minerals,  348 

formation  and  occurrence,  349 

uses  and  production,  348 
Monel  metal,  287 
Monochromatic  light,  99 

interference  with,  112 
Monoclinic  crystals,  angles,  19 

axial  elements,  92 

classes  and  forms,  32  to  35 

charaotersitics,  17 

in  polarized  light,  151 

type  forms,  32 
Mortar,  Leeds,  160 

Negative  crystals,  80 

ray  surfaces,  103,  107 
Nickel,  extraction  of,  287 

summary  of  tests,  191 

see  also,  173,  179.  198,  201 
Nickel  minerals,  286 

formation  and  occurrence,  280 

uses  and  production  of,  287 
Nicol's  prism,  108 

vibration  direction  of,  124 
Nitric  acid,  summary  of  tests,  191 

see  also,  203 

Nitrogen,  minerals  of,  466 
Nodular,  74 

Non-metallic  lustre,  210 
Norite,  251 

Objectives  of  microscope,  118 
Oblique  illumination,  129 
Obtuse  bisectrix,  107 
Oceans,  minerals  formed  in,  254 
Occurrence  of  minerals,  239,  260 

(See  also  iron,   copper,  lead,  etc.) 

of  faces  in  series,  24 
Ochre,  262 

Oculars  of  microscope,  118 
Octahedron,  59 
Odors  in  closed  tubes,  175 

in  open  tubes,  177 

terms  used,  225 
Oil  and  oil-lamps,  159 
Old  gold  veins,  383,  396 


Oolitic,  74 

Opalescence,  211 

Opaque,  213 

Open  tubes,  reactions  in,  176 

Opening  angle,  no 

Optic  axes,  determination  of  angle,  147, 

149 
Dptic  axis,  uniaxial,  102 

biaxial,  105,  106 
Optical  character,  103,  107,  145,  146,  147 
changed  by  expansion,  227 

characters,  96  to  155 

(See    also    under    silicate    groups.) 

constants,  determining,  127 

distinctions  between  systems,  150 

groups,  99 

principal  sections,  106 

tests  with  microscope,  107 
Optically  anistropic  crystals,  100,  127 

biaxial  crystals,  105 

isotropic  crystals,  99,  127 

uniaxial  crystals,  102 
Optic  axial  angle,  107 
Ore  beds,  333 

Organic  sediments,  248,  255 
Organisms,  minerals  formed  by,  255 
Origin  of  minerals,  239-260 
Orthographic  projection,  95 
Ortho  pinacoid,  34 
Orthorhombic  crystals,  angles,  17 
axial  elements,  91 
characteristics,  16 
classes  and  forms,  37-41 
in  polarized  light,  150 
Osmium  uses,  403 

Oxidation  by  means  of  blowpipe,  161 
Oxides,  236 
Oxidizing  flame,  161 

Paints,  262,  296 
Palladium,  uses,  403 
Paragenesis,  239 
Parallel  grouping,  71 

growth,  8 1 

polarized  light,  108 
Paramagnetism,  228 
Parameters,  22 
Parametral  face,  88,  22 
Paris  green,  328 
Partial  symmetry,  12 
Parting,  213 

Path  of  light  in  microscope,  121 
Pearly  lustre,  210 
Pegmatites,  250,  305,  312,  325,  348,  355, 

409,  483,  488 
Penetration  twins,  68 
Penfield's  goniometer,  3 

protractors,  85,  86 
Percussion  figures,  215 
Peridotite,  251 
Pewter,  325 


GENERAL   INDEX. 


621 


Phase  difference,  104 
Phosphorescence,  211 
Phosphorus  summary  of  tests,  181 

see  also,  204 
Phosphorus,  minerals  of,  467 

economic  importance,  467 

formation  and  occurrence,  468 
Physical  characters,  209,  240 
Piezoelectricity,  230 
Pig  iron,  262 
Pinacoid,  see  basal,' brachy,  clino,  macro, 

and  orthopinacoids 
Pisolitic,  74 

Placers  and  gravels,  399,  404 
Plane,  basal,  53 

of  symmetry,  9,  10 

of  vibration,  102 
Plane  polarized  light,  107 
Plaster  tablets,  preparation,  159 

sublimates  on,  171 
Platinum  minerals,  401 

formation  and  occurrence,  404 

production  and  uses,  402 
Platinum  wire  and  holder,  160 
Play  of  color,  211 
Pleochroism,  104,  152 

with  microscope,  153 

with  dichroscope,  154 
Plumose,  74 
Plutonic  rocks,  246 
Pneumatolysis,  242 
Polariscope,  for  axial  angle,  149 
Polarization  in  calcite,  100 

circular,  104 
Polarized  light,  101,  107 
Polarizer  of  microscope,  118 
Polarizing  microscope,  117 
Polysynthetic  twins,  69 
Positive  uniaxial,  103 

biaxal,  107 
Possible  forms,  27 
Potassium,  summary  of  tests,  191 

see  also,  169,  205,  207 
Potassium  minerals,  417 

formation  and  occurrence,  419 

uses  and  production,  417 
Precious  and  ornamental  stones,  550  to 

579 

Precipitation  from  watery  solutions,  243 

Preparation  of  material,  125 

Primary  minerals,  259,  278,  288,  305 

Principal  indices,  104 
optical  section,  106 
vibration  directions,  105 

Prism,  see  brachy,  clino,  dihexagonal, 
ditetragonal,  ditrigonal,  hemi,  hexa- 
gonal, macro,  ortho,  rhombic,  tetra- 
gonal, trigonal 

Prismatic  habit,  76 

Processes  of  formation,  241 

Projection,  clinographic,  92 


Projection,  oblique  faces,  85,  86 

orthographic,  95 

stereographic,  84 

vertical  faces,  85 
Protractors,  Penfield's,  85,  86 
Pseudomorphs,  239 
Pseudo  symmetry,  70 
Pycnometer,  223 

Pyramid,  see  clino,  dihexagonal,  ditetra- 
gonal, hemi,  hemimorphic,  hexagonal, 
orthorhombic,  tetragonal,  trigonal 
Pyramidal  habit,  76 
Pyritohedron,  66 
Pyroelectricity,  230 

Qualitative  blowpipe  analysis,  197 

Quarry  industry,  479 

Quarter  undulation  mica  plate,  135,  146 

Quartz  wedge,  136 

Quartzite,  248 

Quicksilver,  see  mercury 

Radiating  crystals,  72 
Radium  minerals,  341 

luminescence,  212 

tests  for,  195 
Rain  water,  243 
Ray  surface,  biaxial,  105 

positive  and  negative,  -103,  106 
uniaxial,  132 
Reagent  bottles,  160 
Reducing  flame,  162 
Reduction  by  flame,  162 

with  metallic  sodium,  174 

with  soda,  173 
Referring  a  face  to  axes,  21 
Reflection  goniometers,  82 

of  light,  96 

total,  98 
Refraction,  definition,  97 

double,  102,  107 

in  calcite,  100 

index  of,  97,  103,  107,  128,  129,  131, 

132 
Refractometers,  131 

Fuess  simple,  133 

Herbert  Smith,  133 
Reniform,  74 
Repetition,  7 

Replacement,  metasomatic,  245,  258,  264, 
297,  317,  333,  351,  357,  36o,  384,  404, 
452,  469,  521 
Residual  deposits,  265,  279,  298,  306,  312, 

347,  355,  399,  404,  432 
Resinous  lustre,  210 
Retardation,  determining,  136 
Retger's  solution,  225 
Reticulated,  72 
Rhombic  prism,  39 

pyramid,  38 
Rhombohedron  of  the  first  order,  49 


622 


GENERAL   INDEX. 


Rhodium,  uses,  403 
Roasting,  379 
Rocks,  definition,  246 

eruptive,  246 

metamorphic,  248 

plutonic,  246 

sedimentary,  247 

sections  of,  126 

volcanic,  246 
Resetted,  72 

Roughened  faces  of  crystals,  78 
Running  streams,  deposition  by,  254 

Saline  residues,  419,  452,  455,  462 

Salt  of  phosphorus,  reactions  with,  177, 

179 

bead,  how  to  make,  162 
Salts,  chemical,  236 
Sandstones,  247,  480 
Scale  of  hardness,  Moh's,  217 

fusibility,  i>.  Kobell's,  164 
Scalenohedron,  hexagonal,  49 
Schemes  for  blowpipe  analysis,  197-207 

for  determination  of  minerals, 
Scorification,  379 
Sectile,  216 
Secondary  crystallizations,  501 

deposits,  347 

phosphates,  468 

vein  minerals,  260 
Sections  of  crystals,  125 

or  rocks,  126 

oblique,  145 

perpendicular  acute  bisectrix,  143 

perpendicular  optic  axis,  141,  144 
Sediments,  chemical,  248,  253,  483 

due  to  organisms,  248,  255,  483 

mechanical,  247,  253,  483,  489 

marine,  469 

Segregations,  see  magmatic  segregations 
Selenides,  396,  464 
Selenium,  summary  of  tests,  192 

see  also,  171,  172,  173,  176 
Sensitive  tint  plates,  137,  139 
Separation  from   magma,   241,    249  and 
silicate  groups 

from  watery  solutions,  243,  245 
Series,  24,  36,  42 
Shales,  247 
Sheaf  like,  74 
Sienna,  262 
Signal,  84 

Sign  of  elongation,  135 
Silica,  482 

Silicates,  and  their  uses,  479 
Silicates,  rock  forming,  479 
Silicate  magma,  241 
Silicon,  summary  of  tests,  192 

see  also,  173,  202,  205 
Silky  lustre,  210 
Silver  cupellation  test,  378 


Silver  in  manganese  ores,  280 

in  lead  ores,  316 

see  also,  173,  189,  203 

summary  of  tests,  192 
Silver  minerals,  378 

formation  and  occurrence,  382 

uses,  production  and  extraction,  380 
Simple  mathematical  ratio,  law  of,  24 
Skeleton  crystals,  77 
Slate,  248,  480 
Smalt,  286 

Smeeth  specific  gravity  method,  222 
Smith  (Herbert)  refractometer,  133 
Soda,  reactions  with,  172 
Soda  lakes,  minerals  of,  258 
Sodium  carbonate,  172, 
Sodium,  reactions  with,  174 

summary  of  tests,  193 

see  also,  169,  205 
Sodium  minerals,  421 

formation  and  occurrence,  422 

production  and  uses,  421 
Solid  solutions,  234 
Solids  in  ocean  and  rivers,  254 
Solubility  tests,  180 
Solvent  power  of  water,  242 
Solutions,  fusion,  242 

solid,  234 

watery,  242 
Specific  gravity,  218 

determination,  219 

flask,  223 

Spectra,  absorption,  169 
Spectroscope,  use  of,  166 

chart,  168 

Splintery  fracture,  216 
Springs,  minerals  from,  253 
Stalactitic,  74 

Stereographic  projection,  84 
Stfeak,  definition  and  determination,  212 
Striations  of  crystals,  77 
Strontium,  summar3r  of  tests,  193 

see  also,  173,  202,  205,  207 
Strontium  minerals  and  their  uses,  434 

formation  and  occurrence,  435 
Structure,  crystals,  26,  208 

hour  glass,  79 

zonal,  79 
Sublimates  in  closed  or  open  tubes,  176, 

on  charcoal  or  plaster,  171 
Sulphates  of  soda,  423 
Sulphur  deposits,  462 
Sulphur  extraction,  461 

from  pyrite,  etc.,  263 

summary  of  tests,  193 

see  also,  176,  189 
Sulphur  minerals  and  their  uses,  460 

formation  and  occurrence,  462 

from  spring  water,  254 
Sulphuric  acid,  460 
Supports  for  blowpiping,  159 


GENERAL  INDEX. 


623 


Surface  conductivity,  226 
Symbols  of  crystal  faces,  21 

of  forms,  23 

of  Miller,  22 

of  Weiss,  22 

type,  25 
Symmetry  of  crystals,  6 

axes  of,  7,  8,  10 

centre  of,  7,  10 

classes,  n,  25 

determination,  87 

geometric,  7,  10 

partial,  12 

planes  of,  9,  10 

law  of,  7,  9 

Synthesis  of  minerals,  240 
Synthetic  corundum,  556 

diamonds,  553 

turquois,  571 

Systems,  the  six  crystal,  21 
System,  determination,  by  axes,  21 
by  optical  tests,  150 
by  partial  symmetry,  12 

Tables,  mineral  determination,   585-613 

atomic  weights,  614 
Tabular  habit,  76 
Tantalum  minerals,  355 
Tarnish,  definition,  211 
Taste,  terms  used,  225 
Tellurides,  395.  396 
Tellurium,  summary  of  tests,  193 

see  also,  172,  i?3.  i?6 
Tellurium  minerals,  464 
Tenacity,  216 
Tetragonal  crystals,  angles,  15 

axial  elements,  91 

characteristics,  14 

classes  and  forms,  42  to  47 

in  polarized  light,  150 

series,  42,  45 
Tetrahedron,  63 
Tetrahexahedron,  59 
Tetrapyramid,  29 
Thermal  characters,  226 
Thickness  determining,  137 
Thorium  minerals,  310 

formation  and  occurrence,  312 

uses  and  production  of,  311 
Thoulet  solution,  224 
Tin,  summary  of  tests,  194 

see  also,  171,  172,  173,  176,  181,  198, 

199,  202 
Tin  minerals,  304 

economic  importance,  304 

formation  and  occurrence,  305 
Tin  plate,  304 
Titanium,  summary  of  tests,  194 

see  also,  179,  181,  200,  202,  206 
Titanium  minerals,  308 

economic  importance,  308 


Titanium,     formation    and     occurrence, 

308 

Total  reflection,  98 
Tough,  216 
Translucency,  213 
Transparency,  152,  213 
Transmission  of  heat,  226 

of  light,  96 
Trapezohedron,  59 
Triclinic  crystals,  angles,  20 

axial  elements,  91 

characteristics,  19 

classes  and  forms,  29  to  31 

in  polarized  light,  151 
Trigonal  prism,  first  order,  53 
Trisoctahedron,  59 
Tristetrahedron,  63 
Tube  tests,  175,  176 
Tungsten,  summary  of  tests,  194 

see  also,  173,  179,  200 
Tungsten  minerals,  350 

economic  importance,  351 

formation  and  occurrence,  351 
Twin  crystals,  68 

axis,  68 

plane,  69 

symmetry  of,  68 
Twinning,  polysynthetic,  69 
Twins,  contact,  68 

penetration,  68 
Type  faces  in  any  class,  25 

metal,  332 

symbols,  25 
Types,  185 

chemical,  236 

Umber,  262 

Underground  water,    244 
Uniaxial  interference  figures,  141 

oblique  sections,  146 

optical  characters,  103 

ray  surface,  102 

vs.  biaxial,  140 
Uniaxial  crystals,  102 

in  polarized  light,  141 
Unit  face,  36 
Unit  prism,  39 

pyramid,  38 
Universal  stage,  149 
Uranium,  summary  of  tests,  195 

see  also,  179,  201 
Uranium  minerals,  341 

formation  and  occurrence,  342 

uses  and  production,  341 

Van  der  Kolk  test,  129 

Vanadium,  summary  of  tests,  196 
see  also  121,  173,  179,  201 
formation  and  occurrence,   337 
uses  and  production,  336 

Vein  minerals,  primary,  259 


624 


GENERAL   INDEX. 


Vein  minerals,  secondary,  260 

see  under  groups 
Veins,  high  temperature,  259 

pegmatite,  250 
Verneuil's  blowpipe,  556 
Vibration  direction  of  lower  nicol,  124 

in  calcite,  101 

of  faster  and  slower  rays,  134 

see  also  104,  107,  no 
Vibrations,  plane  of,  102 
Vicinal  faces,  25,  78 
Vitreous  lustre,  210 
Volatilization,  elements  affected,  169 

of  light,  96,  101 
Volcanic  exhalations,    vapors    and    acid 

solutions,  410,  439,  455,  462 

rocks,  246 

minerals  of,  497 
Volcanoes,  minerals  near,  250 

Wave  length  of  light,  99 
Water  of  crystallization,  237 

rain,  243 

solvent  power,  243 

tests  for,  175,  205 

underground,  244 
Watery  solutions,  minerals  from,  243 

solids  from,  245 
Weathering  and  weathering  solutions,  247 


Weathering,  minerals  produced  by,  252 
see  saline  residues,  residual  deposits 

and  sediments 
Wedges,  compensating,  136 
Weiss's  parametral  symbols,  22 
Westphal's  balance,  224 
White  lead,  316 
Wire  like,  74 

X-Rays  and  phosphorescence,  211 

Young  gold  and  silver  veins,  382-395 
Yttrium,  production  and  uses,  312 

Zeolites,  252 

Zinc,  summary  of  tests,  196 

see    also,    118,    171,    173,    176,    181, 

198 
Zinc  minerals,  295 

formation  and  occurrence,  297 

uses  and  production  ot,  295 
Zinc  pigments,  296 
Zirconium  minerals,  310 

formation  and  occurrence,  312 
Zonal  determination  of  indices,  88 

structures,  79 
Zone  relations,  88 
Zones,  23 


INDEX  TO  MINERALS. 


Names  of  species  are  in  heavier  type,  varieties  and  synonyms  in  lighter  type; 
the  black  numbers  refer  to  the  descriptions,  the  prefix  t.  is  placed  before  the 
number  of  the  group  of  the  tables  for  determination. 


Acmite,  507.  251. 

Actinolite,  508,  256 

Adamantine,  spar.  413 

Adularia,  252,  493 

Aegirite,  507 

Agate,  574 

Agolite,  546 

Alabandite,  280,  t.  10 

Alabaster,  443,  444 

Alberdte,  478 

Albite,  496,  69,  70,  250,  251,  253,  257,  258, 

260,  494 
Alexandrite,  561 
Allanite,  529,  t.  46,  251 
Allophane,  549.  t.  S3 
Almandine,  558,  567 
Almandite,  510,  249 
Aluminite,  415,  t.  54 
Alum  stone,  416 
Alunite,  416,  t.  55,  252 
Alunogen,  415,  t.  26 
Amalgam,  386,  t.  19 
Amazonite,  577 
Amazonstone,  577 
Amber,  578 
Amber  mica,  540 
Amblygonite,  428,  t.  41,  251 
Ambrite,  478 
Amethyst,  569,  484,  486 
Amphibole,  507,  t.  41,  t.  48,  249,  252,  253, 

256,  257,  258,  260,  501,  503 
Amphibole  group,  500 
Analcite,  531,  t.  42 

Andalusite,  518,  t.  55,  250,  257,  258,  570 
Andalusite  group,  517 
Andesine,  495,  496 
Andradite,  510,  249 
Anglesite,  321,  t.  31,  260 
Anhydrite,  442,  t.  40,  248,  254 
Ankerite,  448 
Annabergite,  294,  t.  27 
Anorthite,  494,  t.  50,  257 
Anorthoclase,  251,  253 
Anthophyllite,  507,  t.  52 
Antigorite,  545 
Antimony,  333,  t.  15 
Antimony  ochre,  335 


Apatite,  470,  t.  51,  250,  251,  258,  260,  467 

Aphthitalite,  t.  25 

Apophyllite,  534,  t.  39 

Aquamarine,  560,  522,  523, 

Aragonite,  444,  t.  56,  69,  70,  254,  255 

Argentine,  448 

Argentite,  386,  t.  5,  259 

Arsenic,  329,  t.  15 

Arsenopyrite,  330,  t.  n,  259,  260 

Asbestus,  509 

Asparagus  stone,  470 

Asphaltum,  478,  474 

Atacamite,  370,  t.  47 

Augite,  505,^506 

Aurichalcite,  301,  t.  29 

Autunite,  345,  t.  47 

Aventurine,  486,  569 

Axinite,  569,  570,  t.  48,  259 

Azurite,  371,  t.  45,  260,  577 

Balas  ruby,  558 

Baddelyite,  312 

Barite,  432,  t.  41,  252,  259 

Barytocalcite,  433,  t.  49 

Bastite,  505 

Bauxite,  413,  t.  54,  253 

Benitoite,  557 

Beryl,  522,  t.  52,  71,  250,  258,  559 

Beryllonite,  562 

Biotite,  540,  t.  51,  t.  52,  250,  256,  257,  258, 

260,  481 

Bismite,  327,  t.  30 
Bismuth,  326,  t.  17,  260 
Bismuth  ochre,  327 
Bismuthinite,  326,  t.  17,  260 
Bismutite,  327,  t.  29 
Black  diamond,  552 

hematite,  283 

jack,  298 

lead,  476 

mica,  540 

opal,  572 

oxide  of  copper,  369 

oxide  of  manganese,  281 
Blende,  298 
Bloodstone,  573 
Blue  carbonate  of  copper,  371 


625 


626 


INDEX  TO  MINERALS. 


Blue  iron  earth,  472 

chrysoprase,  573 

spar,  572 

vitriol,  370 
Bog  iron  ore,  274,  275 

manganese,  283 

Bone  turquois,  571  t 

Boracite,  458,  t.  40,  255 
Borax,  456,  t.  25,  255 
Bornite,  364,  t.  22,  259,  260 
Boronatrocalcite,  457 
Bort,  552 
Boulangerite,  320 
Bournonite,  319,  t.  17 
Braunite,  280,  t.  6,  259 
Brimstone,  463 
Brittle  silver  ore,  389 
Brochantite,  370,  t.  47,  260 
Bromargyrite,  392 
Bromyrite,  392,  t.  31,  260 
Bronze  mica,  540 
Bronzite,  504 

Brookite,  310,  t.  10,  250,  257 
Brown  clay  ironstone,  275 

hematite,  274 
Brucite,  452,  t.  58,  256 
Bytownite,  495 

Cacholong,  573 

Cairngorm,  569 

Calamine,  301,  t.  33,  260 

Calaverite,  400,  259 

Calif ornite,  576,  512 

Calc  spar,  446 

Calcite,  446,  t.  56,  252,  254,  255,  259,  437 

Calomel,  377,  t.  35 

Cancrinite,  t.  38,  251 

Capillary  pyrites,  292 

Carbonado,  552 

Carnallite,  420,  t.  25,  255,  451 

Carnelian,  573 

Carnotite,  344 

Cassiterite,  307,  t.  7,  t.  31,  251,  260 

Cat's-eye,  486,  561,  569 

Celestite,  435,  t.  41,  254,  259 

Celsian,  493 

Cerargyrite,  391,  t.  31,  260 

Cerite,  315,  t.  57 

Cerussite,  323,  t.  29,  260 

Cervantite,  335,  t.  58 

Ceylonite,  558 

Chabazite,  532,  t.  39,  77 

Chalcanthite,  370,  t.  25,  260 

Chalcedony,  486,  t.  59,  254,  259  484,  573 

Chalchihuitl,  572 

Chalcocite,  364,  t.  5,  259,  260 

Chalcopyrite,  365,  t.  22,  251 

Chalk,  448 

Chamosite,  254 

Chiastolite,  257,  80,  518 

Chili  saltpetre,  427 


China  clay,  547 

Chloanthite,  291 

Chlorastrolite,  578 

Chlorite  group,  541,  t.  52,  252,  253,  257, 
258,  259,  482 

Chondrodite,  t.  57,  252 

Chromic  iron,  346 

Chromite,  346,  t,  10,  250,  251 

Chrysoberyl,  560,  t.  55,  251,  258      ; 

Chrysocolla,  372,  t.  58,  260,  572 

Chrysolite,  513,  t.  57,  257,  566 

— oriental,  561 

Chrysoprase,  573 

Chrysotile,  545 

Cinnabar,  376,  t.  35,  254 

Cinnamon  stone,  567 
Citrine,  569 
Clausthalite,  321,  t.  13 
Clay,  482 

Clay  ironstone,  272 
Clinochlore,  542 
Coal,    mineral,  478 
Cobalt  glance,  290 

pyrites,  289 

Cobaltite,  290,  t.  n,  259 
Colemanite,  458,  t.  43 
Columbite,  355,  t.  6.  t.  10,  250 
Common  garnet,  511 
opal,  487 
pyroxene,  506 
Copalite,  478 
Copiapite,  270,  t.  26 

Copper,  362,  t.  24,  72,  75,  250,  251,  260 
Copper  glance,  364 
nickel,  293 
pyrites,  365 
uranite,  345 
vitriol,  370 
Coquimbite,  270,  t.  26 
Cordierite,  529 

Corundum,  412,  t.  55,  249,  251,  258,  554 
Crocidolite,  509,  t.  48 
Crocoite,  347,  t.  30,  260 
Cryolite,  412,  t.  40 
Cuprite,  368,  t.  47,  77,  260 
Cyanite,  519,  t.  55,  251,  257,  258,  557 
Cymophane,  561 

Dammar,  478 
Dark  ruby  silver,  389 
Datolite,  536,  t.  42 
Delessite,  543 
Demantoid,  567 
Descloizite,  339,  t.  30 
Desmine,  533 
Diallage,  507 

Diamond,  550,  t.  59,  250,  251 
Diaspore,  415,  t.  55 
Diatomaceous  earth,  487 
Dichroite,  529 
Diopside,  506,  t.  41,  256,  567 


INDEX   TO   MINERALS. 


627 


Dipyre,  516 

Dog-tooth  spar,  447 

Dolomite,  448,  t.  56,  248,  255,  259,  451 

Dry-bone,  300 

Edenite,  509 

Eisstein,  412 

Elaeolite,  499 

Elaterite,  478 

Electric  calamine,  301 

Embolite,  392,  t.  31,  260 

Emerald,  559,  522,  523, 

Emery,  412,  413 

Enargite,  366,  t.  i,  259 

Enstatite,  504,  t.  52,  256,  501,  503,  567 

Epidote,  528,  t.  48,  252,  253,  256,  258,  567 

Epidote  group,  526 

Epsomite,  453,  t.  26,  452 

Epsom  salt,  453 

Erythrite,  292,  t.  27 

Essonite,  567 

Euclase,  562,  251 

Falcon's  eye,  570 

False  topaz,  486 

Fancy  sapphires,  554 

Fayalite,  515,  249 

Feather  ore,  320 

Feldspars,  488,  492.  249,  250,  481 

Feldspathoids,  497 

Ferberite,  352 

Fergusonite,  356,  t.  59,  251 

Ferruginous  quartz,  486 

Fibrolite,  519 

Fire  opal,  487,  572 

Flint,  486 

Flos  ferri,  444 

Fluorite,  441,  t.  40,  250,  252,  254,  257,  259, 

260,  438 
Fluor  spar,  441 

Fontainebleau  sandstone,  80,  447 
Fool's  gold,  266 
Forsterite,  513,  t.  57,  257 
Franklinite,  302,  t.  7 
Freibergite,  367 
French  chalk,  546 
Fullers  earth,  482 

Gadolinite,  315,  t.  58,  251 

Gahnite,  302,  t.  35 

Galena,  318 

Galenite,  318,  t.  3,  t.  13,  259 

Garnet,  509,  t.  48,  t.  59,  249,  250  256,  258, 

260,  481,  567 
Garnierite,  294,  t.  37,  58 
Gay-Lussite,  427,  t.  38 
Geocronite,  320 
Geyserite,  487 

Gibbsite,  415,  t.  55,  73,  253,  258 
Gilsonite,  478 
Girasol,  573 


Glauber  salt,  426 

Glauberite,  427 

Glauconite,  254 

Glaucophane,  509 

Goethite,  273,  t.  9,  t.  37 

Gold,  399,  t.  24,  250,  251,  259,  260 

Gold  selenides,  396 

Gold  tellurides,  400,  t.  16,  t.  23,  259,  260, 

395 

Golden  beryl,  560 
Goshenite,  523 
Goslarite,  299,  t.  26 
Graphite,  476,  t.  6,  250,  251,  257,  258,  473, 

475 

Gray  antimony,  334 
copper  ore,  367 
Greasy  quartz,  486 
Greenalite,  254 
Greenockite,  303,  t.  32 
Green  carbonate  of  copper,  371 
Grossularite,  510,  256 
Griinerite,  509 
Guano,  469 
Gummite,  344 
Gypsite,  444 
Gypsum,  443,  t.  40,  248,  252,  254,  438 

Halite,  425,  t.  25,  248,  254,  422 

Halloysite,  549,  254 

Harmotome,  534,  t.  40 

Hausmannite,  281,  t.  10,  250,  259 

Hauynite,  500,  497,  498,  249,  557 

Heavy  spar,  432 

Hedenbergite,  506 

Heliodore,  560 

Heliolite,  578 

Heliotrope,  573 

Hematite,  271,  t.  9,  t.  37.  73,  250,  258, 

260,  579 

Hessite,  387,  t.  16 
Heulandite,  534,  t.  40 
Hewettite,  340 
Hiddenite,  565,  429 
Hornblende,  508,  507,  251,  256,  257 
Horn  silver,  391 

mercury,  377 
Horse  flesh  ore,  364 
Huebnerite,  352 
Hyacinth,  563,  567,  314 
Hyalite,  487 
Hyalophane,  493 
Hyalosiderite,  514 
Hydrophane,  573 
Hydrozincite,  300,  t.  32,  254 
Hydrohematite,  274 
Hypersthene,  505,  t.  48,  t.  52,  251,  256, 

501,  503 

Ice,  465 

Iceland  spar,  446,  447 

Idocrase,  511 


628 


INDEX   TO  MINERALS. 


Ilmenite,  273,  t.  4.  t.  9.  250,  251,   258, 

260 

Indianite,  497 
Indicolite,  565 
Indigo  copper,  363 
Infusorial  earth,  481,  487 
lodargyrite,  392 
lodyrite,  392.  t.  31.  260 
lolite,  529,  t.  51,  251,  257,  258,  557 
Indium,  406 
Iridosmine,  406,  t.  19 
Iron,  265,  t.  18,  251 
Iron  pyrites,  266 
Isinglass,  539 

Jacinth,  563 
Jade,  574 
Jadeite,  575 
Jamesonite,  320,  t.  13 
Jargon,  563 
Jeffersonite,  507 
Jasper,  486 
Jeffersonite,  507 
Jet,  579 

Kainite,  420,  t.  25,  255 
Kalinite,  420,  t.  25 
Kaolin,  547 

Kaolinite,  547,  t.  55,  482 
Kermesite,  335,  t.  30 
Kieserite,  453,  t.  26,  255,  451 
Krennerite,  400 
Kunzite,  429,  565 
Kyanite,  519 

Labradorite,  495,  496,  251,  578 

Lapis  Lazuli,  257,  576 

Laterite,  413 

Lazulite,  572 

Lazurite,  576,  t.  39 

Lead,  318 

Lepidolite,  429,  t.  41,  250,  260 

Leucite,  498,  t.  54,  249,  497,  498 

Leucopyrite,  331 

Light  ruby  silver,  388 

Lime  uranite,  345 

Limestone,  446,  448 

Limonite,  274,  t.  9,  t.  37,  74,  253,  254 

256,  260 

Linarite,  322,  t.  31 
Linnaeite,  289,  t.  14 
Lithia  mica,  429 
Lodestone,  270 
Lollingite,  331,  t.  n 
Loxoclase,  493 

Magnesian  limestone,  448 

mica,  540 

Magnesite,  453,  t.  56,  255,  452 
Magnetic  iron  ore,  270 

pyrites,  266 


Magnetite,  270,  t.  4.  77,  250,  251,  253 

258,  260 

Malachite,  371,  t.  45,  260,  578 
Vlanganblende,  280 
Manganite,  282,  t.  10 
Manjak,  478 
Marble,  446,  448 
Margarite,  541,  t.  52 
Marialite,  515 

Marcasite,  268,  t.  22,  70,  256 
Marl,  448 
Vlartite,  272 
Mascagnite,  430 
Matura  diamonds,  563 
VIeerschaum,  546 
Meionite,  515 
Melaconite,  369 
Melanterite,  270,  t.  26 
Melilite,  499,  t.  46,  497,  498 
Menaccanite,  273 
Mercurial  tetrahedrite,  375 
Mercury,  375,  t.  20 
Metacinnabarite,  376,  t.  6 
Metahewettite,  340 
Mica  group,  537,  t.  52,  249,  260,  481 
Microcline,  494,  t.  52,  250,  490 
Milky  quartz,  486 
Millerite,  292,  t.  22,  250 
Mimetite,  323,  t.  27,  260 
Mineral  coal,  478 
Minium,  321,  t.  30 
Mirabilite,  426,  t.  25,  255 
Mispickel,  330 
Misy,  270 
Mizzonite,  516 
Mocha  stone,  574 
Moldavite,  567 

Molybdenite,  349,  t.  16,  250,  251,  260 
Molybdite,  350,  t.  34 
Monazite,  313,  t.  58,  250,  257 
Montmorillonite,  549 
Moonstone,  577 
Morganite,  560 
Moss  agate,  574 
Mottramite,  339 
Mundic,  266 
Muscovite,  539,  t.  52,  250,  258 

Native  antimony,  333 
arsenic,  329 
boric  acid,  456 
bismuth,  326 
copper,  362 
gold,  399 
iron,  265 
lead,  318 
mercury,  375 
platinum,  405 
silver,  385 
sulphur,  463 
tellurium,  465 


INDEX   TO  MINERALS. 


629 


Native  vermilion,  376 

Natrolite,  532,  t.  42 

Needle  zeolite,  532 

Nephelite,  499,  t.  42,  249,  251,  497,  498 

Nephrite,  575 

Niccolite,  293,  t.  21,  259 

Nickel  bloom,  294 

Nigrine,  309 

Nitre,  420,  t.  25,  256 

Noselite,  500,  249,  497,  498 

Noumeite,  294 

Ochre,  red,  272 
yellow,  275 
Octahedrite,  310 
Odontolite,  57* 
Oligoclase,  495,  496 
Olivenite,  t.  27 
Olivine,  5*3 
Olivine  group,  512 
Onofrite,  377,  t.  2 
Onyx,  574,  448 

Opal,  487,  t.  59.  253,  254,  256,  259,  572 
Orangite.  315 
Orpiment,  330,  t.  28,  254 
Orthoclase,  492,  t.  52,  250,  259,  489 
Ozocerite,  477,  473 

Palladium,  406 

Pandermite,  458 

Paragonite,  540 

Pargasite,  256,  509 

Patronite,  338 

Pearl  spar,  448 

Pectolite,  535,  t.  39 

Pencil-stone,  548 

Penninite,  543 

Pentlandite,  292,  t.  22,  250,  251 

Peridot,  513,  566 

Peristerite,  577 

Petalite,  430,  t.  41,  251 

Petroleum,  477,  473 

Petzite,  400,  259 

Phenacite,  562,  t.  55,  251 

Phlogopite,  540,  t.  52,  250,  258 

Phosgenite,  324,  t.  29 

Phosphate  rock,  256,  471 

Phosphorite,  471 

Picotite,  558 

Piedmontite,  528,  258 

Pitchblende,  343,  344 

Plagioclase,  494,  t.  41,  t.  43,  490 

Plagionite,  320 

Platiniridium,  406 

Platinum,  405,  t.  18,  t.  19,  250,  251,  402 

Plumbago,  476 

Plumbocalcite,  448 

Polianite,  282,  t.  6 

Polybasite,  390,  t.  2,  259 

Potash  alum,  420 

Potash  feldspar,  492 


Potash  mica,  539 
Prase,  569 
Precious  opal,  487 

topaz,  564 

Prehnite,  535,  t.  40,  73,  258,  567 
Priceite,  458 
Prochlorite,  543 
Proustite,  388,  t.  28,  259 
Psilomelane,  283,  t.  6 
Psittacinite,  339 
Pucherite,  340 
Purple  copper  ore,  364 
Pyrargyrite,  389,  t.  7,  t.  31,  259 
Pyrite,  266,  t.  22,  68,  75,  77,  250,  251,  256, 

259 

Pyrolusite,  281,  t.  6 
Pyromorphite,  322,  t.  30,  260 
Pyrope,  568,  570,  249 
Pyrophyllite,  548,  t.  52,  258 
Pyroxene,  505,  t.  41,  t.  48,  249,  251,  256, 

258,  260,  501,  503 
Pyroxene  group,  500 
Pyrrhotite,  266,  t.  22,  250,  251 

Quartz,  484,  t.  59,  68,  76,  249,  250,  254, 
257,  259,  480,  484,  568 

Realgar,  329,  t.  28,  254 
Red  antimony,  335 

hematite,  272 

iron  ore,  271 

ochre,  272 

oxide  of  copper,  368 

zinc  ore,  299 
Rensselaerite,  546 
Rhodochrosite,  284,  t.  56,  259 
Rhodolite,  568 

Rhodonite,  284,  t.  48,  259,  579 
Rhyacolite,  493 
Richterite,  509 
Rock  crystal,  568,  484,  486 

gypsum,  444 

meal,  448 

salt,  248,  425 
Roscoelite,  340,  t.  48,  259 
Rose  quartz,  486,  569 
Rubellite,  564 
Rubicelle,  558 
Ruby,  554,  412,  413,  556 

copper,  368 

spinel,  558 

silver,  388,  389 

Rutile,  309,  t.  10,  59,  80,  250,  251,  253, 
257.  258 

Sal  ammoniac,  430,  t.  26 

Salt,  425 
Saltpetre,  420 
Samarskite,  356,  251 
Sanidin,  493,  489 
Sapphire,  554,  412,  413.  555 


630 


INDEX   TO   MINERALS. 


Sapphire,  fancy,  554 

synthetic,  556 
Sapphirine,  558 
Sard,  573 
Sardonyx,  574 
Sassolite,  456,  t.  25,  254 
Satin-spar,  447 
Scapolite  group,  5*5 
Scheelite,  353,  t.  51.  260 
Schefferite,  506 
Schorl,  524 
Schorlomite,  51 1 
Schwatzite,  368 
Selenite,  443.  444 
Semi  opal,  487 
Senarmontite,  335,  t.  30 
Sepiolite,  546,  t.  50 
Sericite,  539.  252,  253 
Serpentine,  544,  t.  51,  71,  253,  257,  258, 

481,  576 

Siderite,  275,  t.  36,  254,  258 
Siliceous  sinter,  487 
Sillimanite,  519,  t.  55,  251,  257,  258 
Silver,  385,  t.  19,  260 
Silver  glance,  386 
Simetite,  578 
Smaltite,  291,  t.  n,  259 
Smithsonite,  300,  t.  32,  260,  572 
Smoky  quartz,  486,  569 
Snow,  465 
Soapstone,  545 

Soda  nitre,  427,  t.  25,  256,  424 
Sodalite,  500,  t.  42,  249,  251,  497,  498,  577 
Sodalite  group,  500 
Spartaite,  448 
Spathic  ore,  275 
Specular  iron,  271 
Sperrylite,  405,  t.  n 
Spessartite,  568,  510,  249 
Sphalerite,  298,  t.  7,  t.  32,  259 
Sphene,  525,  566 

Spinel,  558,  t.  55,  68,  249,  256,  258,  260 
Spodumene,  429,  t.  41,  250,  565 
Stalactite,  448 
Stalagmite,  448 
Stannite,  306,  t.  12 
Star  quartz,  569 
Stassfurtite,  458 

•Staurolite,  520,  t.  59,  251,  257,  258 
Steatite,  545 

Stephanite,  389,  t.  2,  259 
Stibiconite,  335 

Stibnite,  334,  t.  2,  t.  12,  72,  254,  259 
Stilbite,  533,  t.  40 
Stream  tin,  307,  308 
Stromeyerite,  387,  t.  19 
Strontianite,  436,  t.  49 
Succinite,  578 

Sulphur,  463,  t.  35,  254,  256 
Sunstone,  578 
Sylvanite,  400,  259 


Sylvite,  419,  t.  25,  255 

Talc,  545,  t.  52,  253,  257,  258,  481 

Tantalite,  355 

Tellurium,  465,  t.  16 

Tennantite,  368,  t.  i 

Tenorite,  369,  t.  5 

Tephroite,  285,  t.  46 

Terlinguaite,  378 

Tetradymite,  326,  t.  17 

Tetrahedrite,  367,  t.  2,  t.  12,  t.  15,  259, 

378 

Thenardite,  427 
Thomsonite,  534 
Thorianite,  316 
Thorite,  315,  t.  57,  251 
Thuringite,  254 
Thulite,  528,  t.  39,  579 
Tigers  eye,  5?o 
Tiemannite,  377,  t.  12 
Tin  stone,  307 
Tin  pyrites,  306 
Tinkal,  456 
Titanic  iron  ore,  273 
Titanite,  525,  t.  48,  250,  258,  566 
Titan  olivine,  514 

Topaz,  523,  t.  55,  249,  250,  258,  260,  564 
Torbernite,  345,  t.  47 
Touchstone,  486 
Tourmaline,  524,  t.  41,  t.  48,  t.  52,  t.  59, 

249,  250,  252,  256,  257,  258,  260,  564 
Travertine,  254,  448 
Tremolite,  508,  t.  41,  256 
Tridymite,  486,  t.  59,  484 
Tripoli,  481,  487 
Trona,  427,  t.  25,  255 
Troostite,  301 
Turgite,  274,  t.  9,  t.  37 
Turkis,  570 
Turkish  stone,  570 
Turquois,  570,  t.  58 

Uintahite,  478 

Ulexite,  457,  t.  43,  255 

Umber,  275 

Uralite,  500 

Uraninite,  343,  t.  8,  t.  10,  251 

Uvanite,  344 

Uvarovite,  510,  t.  59 

Valencianite,  259,  489 

Valentinite,  335,  t.  30 

Vanadinite,  338,  t.  30,  260 

Vanadium  mica,  340 

Variscite,  572 

Vesuvianite,  511,  t.  48,  252,  256,  258 

Vivianite,  472,  t.  37,  260 

Volborthite,  340 

Wad,  283 
Wagnerite,  471,  t. 
Water,  465 


INDEX   TO   MINERALS. 


Water  sapphire,  55? 

Wavellite,  471,  t.  54 

Wernerite,  515,  t.  40,  251,  256,  258 

White  iron  pyrites,  268 

lead  ore,  323 

mica,  539 

opal,  572 

Willemite,  301,  t.  33 
Witherite,  433,  t.  38 
Wolframite,  352,  t.  9,  260 
Wollastonite,  507,  t.  39,  256,  258 
Wood  tin,  308 
Wulfenite,  350,  t.  30,  260 
Wurtzite,  299,  t.  32 
Wurtzilite,  478 


Xenotime,  313,  t.  59 

Yellow  copper  ore,  365 
Yellow  ochre,  275 
quartz,  486 

Zeolite  group,  529 
Zinc  blende,  298 

vitriol,  299 

bloom,  300 
Zincite,  299,  t.  34 
Zinkenite,  320 

Zircon,  314,  t.  59,  76,  250,  251,  258,  563 
Zircon  favas,  312 
Zirconium  oxide,  312 
Zoisite,  528,  t.  41,  251,  258 


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